Critical Review

Microwave digestion procedures for environmentalmatrices

Kathryn J. Lamble and Steve J. Hill*

Department of Environmental Sciences, University of Plymouth, Drake Circus, Plymouth,UK PL4 8AA

Summary of contents

IntroductionOpen or closed digestion systems?

Closed microwave digestion techniquesOpen digestion techniquesOn-line digestion techniquesChemometricsUniversal digestion procedures

Biological samplesGeological samplesWater samples

ConclusionsReferences

Keywords: Microwave digestion; environmental matrices;review

Steve Hill is Professor of AnalyticalChemistry at the University of Ply-mouth where he is currently Head ofthe Department of EnvironmentalSciences. Until recently he wasChariman of the Atomic Spectros-copy Group of the RSC and cur-rently serves on several of the So-ciety’s committees including Ana-lytical Division Council. In additionhe is on the Editorial Boards of TheAnalyst, JAAS, and Analytical Com-munications and is General Ed-itor of Atomic Spectrometry Updates. His research interests arevaried and to date he has over 120 scientific publications basedon analytical chemistry and has made over 150 conferencepresentations.

Introduction

Quantitative analytical techniques are required to determineaccurately and rapidly a variety of trace metals with sufficientsensitivity for application to a range of environmental samples.This requirement has led to major technological advances in thedevelopment of analytical instrumentation, enabling vastamounts of elemental information to be obtained in a shortertime and with increased sensitivity than was ever possiblebefore. This is especially true of analytical techniques such asinductively coupled plasma atomic emission spectrometry(ICP-AES) and inductively coupled plasma mass spectrometry(ICP-MS), which can obtain multi-element information in afraction of the time needed to prepare the samples. However,prior to analysis by most analytical techniques there is an

intrinsic requirement for the sample to be converted into a liquidform. For solid samples this can be achieved by undertakingsome form of digestion procedure.

To be effective, sample digestion methods must efficientlydecompose the sample matrix so that the analytes of interest arecompletely released and solubilised and are in a form compat-ible with the analytical method of choice. Effective methods ofsample digestion are therefore a crucial prerequisite to accurateanalysis. However, technological advances in this area havebeen slow in comparison with the developments in analyticalinstrumentation. Until relatively recently, sample digestionmethods were largely limited to the conventional techniques ofwet digestion, dry ashing and fusion techniques. Such methodsare often time consuming, may be the source of contaminationand losses of analyte and generally require a great deal ofoperator attention, skill and experience in order to gain accurateand precise results. As a consequence, sample preparation isoften regarded as the weak link in sample analysis, and an areawhich provides much scope for improvement.

Significant improvements in sample preparation techniqueshave been made since 1975, however, when Abu-Samra1 firstreported the use of microwaves as a heat source for wetdigestion methods. Since then the microwave digestion tech-nique has gradually gained widespread acceptance as aneffective method of sample preparation. Using this technique,not only have digestion times been dramatically reduced (by afactor of 2–5) but also other benefits such as a reduction incontamination, less reagent and sample usage, a reduction in theloss of volatile species and improved safety have beenreported.2 The advantages of the microwave digestion tech-nique have led to its application as an effective samplepreparation method for a wide range of sample matrices. Eachyear more and more laboratories replace the conventionalmethods with the new technology, as is reflected in the everincreasing amount of material published on the subject. Anumber of review articles and books have been published2–9

detailing the use of the technique for elemental analysis. Kuss5

listed the applications of microwave digestion techniques forelemental analyses cited in the literature before 1992. Includedwere references for the digestion of biological, geological,environmental and metallic materials. A publication by Zlo-torzynski3 discusses the fundamental principles of microwavefield interaction with the sample matrix, whereas de la Guardiaand Morales-Rubio4 discuss the modern strategies available forthe rapid determination of metals in sewage sludges. A reviewon the use of microwave assisted sample preparation inanalytical chemistry has been undertaken by Smith andArsenault9 and specifically for analysis by electrothermalatomic absorption spectrometry by Chakraborty et al.6

This paper reviews the application of microwave energy forthe digestion of environmental samples (biological, geologicaland water) reported since 1992. Where it was felt that the

Analyst, July 1998, Vol. 123 (103R–133R) 103R

methodological approach would benefit the reader, matriceswhich are not strictly environmental are also included, e.g.,bovine liver, foodstuffs. Details of the open and closedmicrowave digestion methods used to digest these samples,including the advantages and disadvantages of each technique,are discussed. The review also attempts to highlight any trendsin research and to identify universal digestion procedures forparticular matrices or elements.

Tables 1, 2 and 3 summarise the different microwavedigestion procedures employed during the review period forbiological, geological and water samples, respectively. Eachtable characterises the matrix digested, elements determined,microwave system used, digestion method, i.e., specific rea-gents and heating time, and analytical technique used, andfinally comments on the effectiveness of the method. In manycases certified reference materials have been used for validationof digestion procedures. It was observed that results are oftenclassed as ‘good’ when in fact they lie outside the uncertaintylimits of the certified value. For clarification, in this review,results described as ‘good’ indicate that they lie within theuncertainty limits of the certified value. In most cases this isdefined as twice the standard deviation of the mean of thecertified value. Other results are classified as ‘low’ or ‘high’accordingly. A key to the abbreviations used in Tables 1–3 isgiven in Table 4.

Open or closed digestion systems?

During the review period, most studies have concentrated on thedevelopment of closed digestion methods. Most commonlythese are carried out in multimode ovens, in which themicrowaves are dispersed into a large cavity, in a similarmanner as for domestic microwave ovens. Multimode ovenshave also been used for open digestions; however, the majorityof open vessel applications utilise monomode (focused) micro-wave ovens. In the latter case, microwave energy is directlyapplied to the sample by placing it within the waveguide.Hence, it may be better to describe microwave ovens in terms ofthe type of applicator used, i.e., ‘cavity’ for multimode and‘waveguide’ for monomode ovens. A commercial closedmonomode microwave digestion system is also available.27

Each microwave digestion system has certain advantages anddisadvantages, so it is not possible to suggest either as being themost suitable for all applications.

Closed microwave digestion techniques

The closed digestion technique involves placing the sample in avial (or bomb), usually constructed of a fluorinated polymer,such as polytetrafluoroethylene (PTFE) or perfluoroalkoxy(PFA). After adding the digestion reagents, the bomb is tightlysealed and placed in the microwave oven for irradiation bymicrowave energy. Initial closed vessel research was under-taken in domestic multimode microwave ovens. Digestionvessels were often placed inside evacuated desiccators or largeplastic jars to contain the evolved acid vapours and improvesafety in the event of overheating. In order to prevent damage tothe magnetron from reflected microwaves unabsorbed by smallsamples, an additional load (usually water) was commonlyplaced in the microwave oven. However, as these auxiliaryloads reduce the amount of microwave energy reaching thesample, a constant and reproducible supply cannot be guaran-teed. A further disadvantage of the use of domestic microwaveovens is that the power output of the magnetron is static, theoutput being controlled by cycling the magnetron off and on toobtain an average power level. Domestic ovens typically have ahigh time base, generally between 10 and 30 s. Hence, to obtain50% power, the magnetron will only be on for half of the timebase. This approach may prove undesirable for analytical workas significant heat losses can occur during the periods of zero

power output. As a result of the unsuitability of domestic ovensfor use in analytical chemistry, a number of commercial systemshave been specially developed to overcome the problems ofacid fume damage, sample power reflection, field inhomogene-ity, long time bases and safety.29,63,75,79,168,169

The major advantage of the closed microwave digestiontechnique is the high heating efficiency which can be obtained.Heating causes an increase in pressure, due to the evaporation ofdigestion acids and the gases evolved during the decompositionof the sample matrix. This is beneficial by increasing theboiling-point of the reagents, which aids the breakdown of thesample matrix. However, the excessive build-up of pressure,especially during the digestion of samples with a high organiccontent, can lead to the rupture of sealed vessels. For thisreason, most digestion bombs are fitted with pressure reliefvalves, designed to open when the pressure becomes too great,and thus maintain safety. If venting does occur, sample lossesare likely and owing to the reduction in acid vapours a lessactive digestion may result. Considerable research has thereforebeen undertaken to find ways of controlling or reducingpressure build-up during the digestion proc-ess.31,34,42,47,92,101,112,120,123,128,187

One method of avoiding excess pressure is to pre-digest thesample, and thus enable the gases evolved from the decomposi-tion of easily oxidised organic matter to escape beforecommencing the closed digestion procedure. This may becarried out by leaving the samples to pre-digest at roomtemperature, often overnight.31,45,47,49,75,80,92,112,123,128 How-ever, if high sample throughput is required this extra step mustbe taken into account since a large number of digestion vesselswill be required. Pre-digestion can also be carried out bymicrowave heating in an unsealed vessel, prior to the cappingand digestion of the sample in the usual manner. Rhoades49 pre-digested samples by heating for 1 h with a heat lamp. However,an important consideration is that the pre-digestion step shouldnot be too lengthy since it may counteract the benefit of rapiddigestion using microwave systems. Also, excessive evapora-tion of digestion reagents and volatile elements must beavoided. Reid et al.47 overcame these problems by employingan open vessel heptane-cooled reflux pre-digestion step duringwhich oxidation products could escape whilst retaining theanalytes and digestion reagents for the ensuing closed diges-tion.

Heltai and Peresich101 investigated the idea of controlling thevapour pressure by means of a water cooled spiral inserted intothe closed space of the digestion bomb. During the digestion,the acid and water vapours evolved are condensed on the spiral,producing a reflux action which continuously renews the liquidphase over the sample for effective digestion. A differentapproach involves leaving the closed digestion to continuespontaneously after initial heating to induce the reaction. Usingthis method temperatures greater than 150 °C and pressures inexcess of 150 lb in22 were achieved, sufficient, for example, todigest NIST Bovine Liver.120

Another technique reported in order to control pressure build-up is to monitor the pressure or temperature throughout thecourse of the reaction and subsequently apply microwave poweronly when the readings are below the required level. In this waythe pressure can be controlled, thus minimising venting of thedigestion vessel. One commercial company has achieved this byplacing a pressure transducer inside one of the digestion vesselsto monitor the pressure continuously.34 Other workers havetaken temperature measurements using a non-invasive infraredprobe attached to the bottom of the microwave oven.42 In thiscase the output from the probe is fed to a computer whichswitches the magnetron on and off to achieve a pre-settemperature–time programme. The technology for monitoringthe temperature or pressure of the digestion offers the potentialto produce far more reproducible and controllable procedures.

104R Analyst, July 1998, Vol. 123

Tab

le 1

Mic

row

ave

dige

stio

n pr

oced

ures

for

bio

logi

cal

sam

ples

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Bio

logi

cal

tissu

esSe

Prol

abo

(Par

is, F

ranc

e)M

icro

dige

st 3

01 (

200

W)

Ope

n fo

cuse

d H

NO

3–H

2O

2

dige

stio

n fo

r 20

min

(n

= 1

)FI

–CSV

Goo

d re

cove

ries

wer

e ob

tain

ed f

or S

e in

BC

R L

yoph

ilise

d Pi

gK

idne

y10

Mar

ine

biol

ogic

altis

sues

As

Prol

abo

A32

0 (2

00 W

)So

lubi

lisat

ion:

HN

O3

open

focu

sed

dige

stio

n fo

r 10

min

.M

iner

alis

atio

n: H

NO

3–H

2SO

4–

HN

O3–H

2O

2di

gest

ion

for

70m

in

ICP-

MS

and

HPL

C–I

CP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or to

tal a

rsen

ic in

BC

R C

od M

uscl

eaf

ter

both

sol

ubili

satio

n an

d m

iner

alis

atio

n pr

oced

ures

11

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

SePr

olab

o M

icro

dige

st A

301

(200

W)

Ope

n fo

cuse

d H

NO

3di

gest

ion

for

20 m

in, f

ollo

wed

by

addi

tion

of H

2O

2an

d fu

rthe

r he

atin

g fo

r25

min

(n

= 1

)

SeV

Iis

red

uced

to

SeIV

prio

r to

ana

lysi

s by

GC

–MS

Goo

d ag

reem

ent w

ith c

ertif

ied

valu

es fo

r NIS

T B

ovin

e L

iver

and

Mix

ed D

iet

(Fin

land

), a

lthou

gh f

or N

IST

Tot

al D

iet

resu

ltsw

ere

slig

htly

low

. Pro

cedu

re w

as q

uick

er t

han

a co

nven

tiona

lm

etho

d w

ithou

t ne

edin

g H

ClO

4

12

Fat-

rich

foo

dsC

u, F

e, N

i, Z

nPr

olab

o M

icro

dige

stM

300

(200

W)

and

dom

estic

ove

n (7

00 W

)

Clo

sed:

HN

O3–H

2O

2PT

FE b

omb

dige

stio

n fo

r 20

min

.O

pen

focu

sed:

HN

O3–H

2SO

4–

HN

O3

dige

stio

n fo

r 25

min

(n=

1)

FAA

S an

d E

TA

AS

(for

Ni)

For t

he c

lose

d di

gest

ion,

reas

onab

le a

gree

men

t was

obt

aine

d w

ithre

sults

fro

m a

wet

pre

ssur

e au

tocl

ave

dige

stio

n m

etho

d (f

orso

ybea

n fl

our

and

linse

ed s

ampl

es).

How

ever

, re

sults

wer

ege

nera

lly l

ow f

or t

he o

pen

mic

row

ave

met

hod

13

Food

sN

Prol

abo

Max

idig

est

MX

-35

0 (3

50 W

) O

pen

focu

sed

H2SO

4–H

2O

2

Kje

ldah

l ni

trog

en d

iges

tion

for

20–4

5 m

in d

epen

ding

on

food

type

(n

= 1

)

NH

3tit

ratio

nSu

bsta

ntia

l tim

e sa

ving

s ov

er

conv

entio

nal

met

hods

w

ere

dem

onst

rate

d, w

ithou

t th

e ne

ed f

or a

cat

alys

t. H

owev

er,

for

new

mat

rice

s ea

ch s

tep

of th

e pr

oced

ure

mus

t be

re-o

ptim

ised

sepa

rate

ly

14

Cer

eals

and

cere

alpr

oduc

ts

Cd,

Cu,

Pb,

Se

Prol

abo

Mic

rodi

gest

A30

1an

d C

EM

(Buc

king

ham

, UK

)M

DS-

2000

(63

0W

)

(a)

Ope

n fo

cuse

d H

NO

3–H

2O

2

dige

stio

n fo

r 17

min

(n

= 1

).(b

) C

lose

d H

NO

3di

gest

ion

for

60m

in (

n=

12)

ET

AA

SG

ener

ally

goo

d re

sults

wer

e ob

tain

ed f

or t

he o

pen

and

clos

edm

etho

ds f

or B

CR

Bro

wn

Bre

ad,

NR

CC

RM

Whe

at a

nd R

ice

Flou

r, C

GC

Who

le W

heat

and

NIE

S R

ice

Flou

r, C

orn

Bra

n,D

urum

Whe

at F

lour

, H

ard

Red

Spr

ing

Whe

at F

lour

, So

ftW

inte

r W

heat

Flo

ur, R

ice

Flou

r an

d W

heat

Flo

ur

15

Mar

ine

biol

ogic

altis

sues

As,

Cd,

Cu,

Mg,

Mn,

Ni,

Sr, Z

n

Prol

abo

Mic

rodi

gest

A30

1O

pen

focu

sed

HN

O3

dige

stio

n fo

r17

min

, fol

low

ed b

y 20

min

cool

ing

and

furt

her

heat

ing

with

H2O

2fo

r 5

min

(n

= 1

)

ICP-

MS

Gen

eral

ly

good

re

sults

w

ere

obta

ined

fo

r N

RC

C

LU

TS-

1,D

OR

M-1

D

ogfi

sh

Mus

cle,

D

OL

T-2

D

ogfi

sh

Liv

er

and

TO

RT

-1 L

obst

er H

epat

opan

crea

s, e

xcep

t fo

r hi

gh A

s an

d N

i

16

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

Cd

Prol

abo

Mic

rodi

gest

A30

1O

pen

focu

sed

HN

O3–H

2O

2

dige

stio

n fo

r 42

min

ET

AA

S G

ood

resu

lts w

ere

obta

ined

for

NIS

T W

heat

Flo

ur a

nd B

ovin

eL

iver

, alth

ough

for

IA

EA

Fis

h Fl

esh

Hom

ogen

ate

resu

lts w

ere

slig

htly

lo

w.

Acc

epta

ble

agre

emen

t w

ith

resu

lts

from

a

conv

entio

nal

wet

dig

estio

n w

as o

btai

ned

for

bovi

ne m

uscl

e,bo

vine

liv

er,

oyst

er,

barl

ey s

traw

, ca

bbag

e, c

arna

tions

, oa

kle

aves

, pin

e ne

edle

s, a

pple

-fru

it an

d gr

ass

mea

l

17

Bio

logi

cal

tissu

esB

i, C

d, C

o, C

s,C

u, F

e, H

g,M

n, M

o, P

b,R

b, S

b, S

n,Sr

, Tl,

Zn

Prol

abo

Mic

rodi

gest

A30

1an

d M

ilest

one

(Sor

isol

e, I

taly

) M

EG

A12

00 (

1200

W)

HN

O3–H

2O

2di

gest

ion.

Clo

sed

vess

el:

26.5

min

.O

pen

focu

sed:

45

min

ICP-

MS

Ope

n fo

cuse

d: g

ood

resu

lts w

ere

obta

ined

for

NIS

T B

ovin

eL

iver

, exc

ept

for

low

Cu,

Sr

and

Zn.

Clo

sed

vess

el: G

ood

resu

lts w

ere

obta

ined

, exc

ept f

or lo

w C

d, P

ban

d Sr

18

Bio

logi

cal

tissu

esA

s, B

a, C

a,C

d, C

u, F

e,K

, Mg,

Mn,

Na,

P, P

b,Sr

, Zn

Prol

abo

Mic

rodi

gest

M30

0 an

d Fl

oyd

(Lak

eW

ylie

, SC

, USA

) R

MS-

150

(600

W)

Ope

n fo

cuse

d ve

ssel

:H

NO

3–H

2SO

4–H

2O

2–

NH

4E

DT

A d

iges

tion

for

30m

in (

n=

1).

Clo

sed

vess

el:

HN

O3

dige

stio

n fo

r 32

min

ICP-

AE

S an

d re

sidu

alca

rbon

con

tent

ana

lysi

s.G

ener

ally

goo

d re

sults

wer

e ob

tain

ed f

or t

he o

pen

dige

stio

n of

NIS

T B

ovin

e L

iver

and

Oys

ter

Tis

sue,

IA

EA

Hor

se K

idne

yan

d N

IES

Mus

sel T

issu

e, a

lthou

gh N

a re

cove

ries

wer

e sl

ight

lylo

w. T

he r

esid

ual c

arbo

n co

nten

t of

dige

sts

follo

win

g th

e op

enm

etho

d w

ere

far

supe

rior

to

thos

e fr

om t

he c

lose

d sy

stem

19

Tea

lea

ves

Al,

Ba,

Ca,

Cu,

K, M

g, M

n,Z

n

Prol

abo

Mic

rodi

gest

301

Ope

n fo

cuse

d H

NO

3–H

ClO

4

dige

stio

n fo

r 35

min

(n

= 1

)IC

P-A

ES

Goo

d ag

reem

ent

with

the

cer

tifie

d va

lues

for

NIE

S T

ea L

eave

sw

as o

btai

ned

20

Analyst, July 1998, Vol. 123 105R

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Mar

ine

biol

ogic

altis

sues

As

Prol

abo

Mic

rodi

gest

301

On-

line

syst

em i

ncor

pora

ting

HPL

C s

epar

atio

n; p

otas

sium

pers

ulfa

te–N

aOH

oxi

datio

n an

dl-

cyst

eine

pre

-red

uctio

n of

As

spec

ies

in f

ish

sam

ples

follo

win

g en

zym

atic

ext

ract

ion

On-

line

anal

ysis

by

HG

–A

AS.

Tot

al A

s ca

n be

dete

rmin

ed b

y re

mov

alof

the

HPL

C c

olum

nfr

om t

he s

yste

m

The

AsB

et, D

MA

, MM

A, A

sVan

d to

tal a

rsen

ic c

onte

nt o

f NR

CC

TO

RT

-1

Lob

ster

H

epat

opan

crea

s an

d D

OR

M-1

D

ogfi

shM

uscl

e w

ere

dete

rmin

ed b

y th

e on

-lin

e te

chni

que.

Res

ults

for

tota

l ar

seni

c w

ere

in g

ood

agre

emen

t w

ith t

hose

obt

aine

d by

ICP-

MS

anal

ysis

21

Mar

ine

biol

ogic

alsa

mpl

es

As

Prol

abo

Mic

rodi

gest

301

Ope

n fo

cuse

d H

NO

3–H

2O

2

dige

stio

n fo

r 15

min

(n

= 1

)IC

P-M

SG

ood

resu

lts w

ere

obta

ined

for

As

in N

RC

C D

OR

M-1

Dog

fish

Mus

cle

and

TO

RT

-1 L

obst

er H

epat

opan

crea

s21

Mar

ine

biol

ogic

altis

sues

Hg

Prol

abo

Mic

rodi

gest

301

On-

line

dige

stio

n of

0.1

5%sl

urri

es (

in 5

0% H

Cl)

,in

clud

ing

Br2

–BrO

32

oxid

atio

n of

org

anom

ercu

rysp

ecie

s

On-

line

anal

ysis

by

CV

-A

FSA

rec

over

y of

97%

was

obt

aine

d fo

r a

stan

dard

sol

utio

n of

met

hylm

ercu

ry c

hlor

ide.

Res

ults

for

Hg

in N

RC

C D

OR

M-2

Dog

fish

Mus

cle

wer

e in

goo

d ag

reem

ent

with

the

cer

tifie

dva

lue

22

Mar

ine

biol

ogic

altis

sues

Hg

Prol

abo

Mic

rodi

gest

301

Ope

n fo

cuse

d H

NO

3–H

2SO

4–

H2O

2di

gest

ion

for

25 m

in(n

= 1

)

CV

-AA

SG

ood

resu

lts w

ere

obta

ined

for

Hg

in N

RC

C D

OR

M-2

22

Mar

ine

biol

ogic

altis

sues

As,

Cd,

Co,

Cr,

Cu,

Fe,

Mn,

Ni,

Pb, S

e,Sr

, Zn

Prol

abo

Max

idig

est

M40

1(3

00 W

)O

pen

HN

O3

or H

NO

3–

H2SO

4di

gest

ion

for

20–1

00m

in (

depe

ndin

g on

sam

ple

size

) fo

llow

ed b

y ev

apor

atio

nto

a v

olum

e of

1 m

l

ET

AA

SSa

mpl

es o

f up

to 8

g w

ere

succ

essf

ully

dig

este

d. G

ener

ally

goo

dre

sults

w

ere

obta

ined

fo

r N

RC

C

TO

RT

-1

Lob

ster

Hep

atop

ancr

eas

and

LU

TS-

1

23

Sew

age

slud

geH

gPr

olab

o M

icro

dige

st 3

01O

n-lin

e di

gest

ion

of s

lurr

ies

prep

ared

in

nitr

ic a

cid

On-

line

FI–C

V-A

FSG

ood

resu

lts w

ere

obta

ined

for

BC

R S

ewag

e Sl

udge

(D

omes

tic);

how

ever

, res

ults

for

BC

R S

ewag

e Sl

udge

Am

ende

d So

il w

ere

slig

htly

low

24

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

Al,

As,

Cd,

Co,

Cr,

Cu,

H

g,M

g, M

o, N

i,Pb

, Zn

Prol

abo

Mic

rodi

gest

A30

0(2

00W

)O

pen

focu

sed

dige

stio

n w

ith(a

) H

NO

3–H

2O

2,

(b)

HC

l–H

NO

3–H

2O

2,

(c)

HN

O3–H

2SO

4–H

2O

2

ICP-

AE

S an

d IC

P-M

S G

ood

resu

lts w

ere

obta

ined

for

pro

cedu

re (

a) f

or B

CR

Spr

uce

Nee

dles

(ex

cept

low

Al,

Mg)

, W

hite

Clo

ver,

Cod

Mus

cle

(exc

ept

low

Hg)

and

Pla

nkto

n (e

xcep

t hi

gh H

g an

d lo

w M

n).

Proc

edur

e (b

) gav

e hi

gh A

s an

d lo

w M

n, w

here

as p

roce

dure

(c)

gave

low

Hg

resu

lts f

or B

CR

Cod

Mus

cle.

Res

ults

by

(b)

wer

ege

nera

lly l

ow f

or B

CR

Pla

nkto

n, e

xcep

t fo

r C

d, Z

n

25

Bio

logi

cal

tissu

esSb

IIIan

d Sb

VPr

olab

o M

icro

dige

st 3

01O

pen

focu

sed

dige

stio

n w

ith(a

) 1

mac

etic

aci

d (f

or S

bIII ),

(b)

H2SO

4–K

I (f

or t

otal

Sb)

HG

–AA

SG

ood

resu

lts w

ere

obta

ined

for

tot

al S

b in

spi

ked

calv

e liv

ersa

mpl

es. S

bVw

as c

alcu

late

d as

the

diff

eren

ce b

etw

een

tota

l Sb

and

SbII

I

26

Bio

logi

cal

tissu

esH

gPr

olab

o M

icro

dige

st A

301

and

Supe

rdig

est

(300

W)

Ope

n: H

NO

3–H

2SO

4–H

NO

3–

H2O

2di

gest

ion

for

20 m

in(n

= 1

).C

lose

d: H

NO

3di

gest

ion

CV

-AA

SG

ood

resu

lts w

ere

obta

ined

for H

g in

BC

R P

ig K

idne

y an

d IA

EA

Fish

Tis

sue

follo

win

g bo

th m

etho

ds.

For

the

open

met

hod,

dige

stio

n w

ith

just

H

NO

3an

d w

ith

HN

O3–H

2SO

4-H

NO

3

resu

lted

in l

ow r

ecov

erie

s

27

Mar

ine

biol

ogic

altis

sues

Hg

Prol

abo

Mic

rodi

gest

A30

1O

pen

focu

sed

mic

row

ave

assi

sted

extr

actio

n fo

r 2

min

(n

= 1

)w

ith (

a) 2

5% T

MA

H,

(b)

met

hano

lic K

OH

HG

–CT

–GC

–ET

AA

SG

ood

resu

lts w

ere

obta

ined

for

tot

al H

g an

d m

ethy

lmer

cury

in

NR

CC

D

OR

M-1

D

ogfi

sh

Mus

cle

and

TO

RT

-1

Lob

ster

Hep

atop

ancr

eas

and

in B

CR

CR

M 4

63 T

una

Fish

Mus

cle

28

Mar

ine

biol

ogic

altis

sues

Cd,

Cu,

Zn

CE

M M

DS-

81D

(60

0 W

)H

NO

3lo

w v

olum

e T

eflo

n bo

mb

dige

stio

n fo

r 49

min

(n

= 2

4)FA

AS

and

ET

AA

S (f

orC

d)G

ood

resu

lts w

ere

obta

ined

for

Cu,

Zn

and

Cd

in N

IST

Oys

ter

Tis

sue,

NR

CC

DO

LT

-1 D

ogfi

sh L

iver

and

TO

RT

-1 L

obst

erH

epat

opan

crea

s, f

or C

u an

d Z

n in

NR

CC

DO

RM

-1 a

nd f

or Z

nin

NIS

T A

lbac

ore

Tun

a

29

Bot

anic

alsa

mpl

esC

a, C

u, F

e, K

,M

g, M

n, N

a,P,

Zn

CE

M M

DS-

2100

(95

0 W

)H

NO

3–H

Cl

Tef

lon

bom

bdi

gest

ion

for

74 m

in (

n=

12)

ICP-

AE

SG

ood

resu

lts w

ere

obta

ined

for

K,

Na,

P a

nd P

b in

NIS

T S

RM

1572

Citr

us L

eave

s; h

owev

er C

a, C

u, M

g an

d Z

n re

sults

wer

esl

ight

ly l

ow a

nd F

e w

as v

ery

low

. R

esul

ts f

or c

orn

sam

ples

wer

e co

mpa

red

with

the

pac

kage

lab

el c

laim

s of

the

sup

plie

r

30

106R Analyst, July 1998, Vol. 123

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Bot

anic

alsa

mpl

esB

, Se

CE

M

MD

S-20

00 (

630

W)

Se:

HN

O3–H

2O

2–H

2O

PT

FEbo

mb

dige

stio

n fo

r 30

min

follo

win

g pr

e-di

gest

ion

for

4 h.

B:

HN

O3–H

2O

2PT

FE b

omb

dige

stio

n fo

r 45

min

fol

low

ing

pre-

dige

stio

n fo

r 4

h (n

= 1

2)

FAA

S (f

or S

e) a

nd I

CP-

AE

S (f

or B

)Se

reco

veri

es fo

r NIS

T W

heat

Flo

ur w

ere:

23%

with

HN

O3, 3

0%w

ith H

NO

3–H

2O

2,

57%

with

HN

O3–H

2O

2an

d 80

% w

ithH

NO

3–H

2O

2–H

2O

. B re

cove

ries

for N

IST

App

le L

eave

s w

ere:

60%

with

HN

O3

and

66–9

6% w

ith H

NO

3–H

2O

2.

Lon

ger

dige

stio

n tim

es

or

addi

ng

HC

l (f

or

Se)

did

not

incr

ease

reco

veri

es

31

Bot

anic

al a

ndsl

udge

sam

ples

PbC

EM

Spe

ctro

Prep

(550

W)

On-

line

mic

row

ave

dige

stio

n of

slur

ried

sam

ples

(pr

epar

ed i

n3

mH

NO

3fo

r bo

tani

cal

and

HN

O3–H

ClO

4–H

F fo

r sl

udge

sam

ples

), 1

0 m

in p

er s

ampl

e

Off

-lin

e an

alys

is b

yID

–IC

P-M

SG

ood

resu

lts w

ere

obta

ined

for

Pb

in N

IST

SR

M 1

547

Peac

hL

eave

s an

d SR

M 2

781

Dom

estic

Slu

dge

32

Coc

oa

Cu,

Fe

CE

M M

DS-

81H

NO

3bo

mb

dige

stio

n fo

r 30

min

(n=

7)FA

AS

The

mic

row

ave

dige

stio

n pr

oced

ure

was

fou

r tim

es q

uick

er th

ana

conv

entio

nal

hot-

plat

e m

etho

d.

Res

ults

fr

om

the

two

tech

niqu

es w

ere

in g

ood

agre

emen

t

33

Bio

logi

cal

tissu

esC

a, F

e, M

g, Z

nC

EM

MD

S-81

H

NO

3bo

mb

dige

stio

n fo

r 30

min

(n=

7)FA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or F

e an

d M

g in

IA

EA

Hor

seK

idne

y, h

owev

er, Z

n re

sults

wer

e sl

ight

ly h

igh

and

Ca

low

34

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Ca,

Cd,

Fe,

Mg,

Zn

CE

M M

DS-

81O

n-lin

e st

oppe

d-fl

ow d

iges

tion

(for

5 m

in)

of s

lurr

ies

(pre

pare

d in

Tri

ton

X-1

00 a

ndH

NO

3)

Off

-lin

e an

alys

is b

y A

AS

Goo

d Z

n re

sults

wer

e ob

tain

ed in

IA

EA

Hor

se K

idne

y, b

ut th

ose

for

Fe a

nd C

d w

ere

low

and

Mg

was

hig

h. T

he s

yste

m w

asun

suita

ble

for

Ca

dete

rmin

atio

ns. R

esul

ts f

or b

atch

mic

row

ave

dige

stio

n, o

n-lin

e m

icro

wav

e di

gest

ion

and

hot-

plat

e di

gest

ion

of

coco

a po

wde

r w

ere

in

good

ag

reem

ent.

Atte

mpt

s at

slur

ryin

g N

IST

Pin

e N

eedl

es, O

yste

r T

issu

e an

d B

ovin

e L

iver

at

conc

entr

atio

ns

need

ed

for

FAA

S de

tect

ion

wer

eun

succ

essf

ul

35

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Ca,

Fe,

Mg,

Zn

CE

M M

DS-

81O

n-lin

e di

gest

ion

of H

NO

3

slur

ries

On-

line

anal

ysis

by

FAA

SG

ood

reco

veri

es a

nd p

reci

sion

was

obt

aine

d fo

r th

e re

sults

of

NIE

S C

hlor

ella

, Sa

rgas

so a

nd P

eppe

rbus

h an

d N

IST

Bov

ine

Liv

er, a

lthou

gh f

or N

IES

Mus

sel,

prec

isio

n w

as s

light

ly h

igh.

At

the

max

imum

sta

ble

slur

ry c

once

ntra

tion,

Zn

was

not

dete

ctab

le b

y FA

AS

in C

hlor

ella

and

Sar

gass

o, n

or w

as C

a in

Bov

ine

Liv

er

36

Mar

ine

biol

ogic

altis

sues

SeC

EM

MD

S-81

HN

O3–H

2O

2bo

mb

dige

stio

n fo

r24

min

fol

low

ed b

yev

apor

atio

n to

nea

r dr

ynes

s (4

5m

in)

ET

AA

SR

esul

ts fo

r Se

in ly

ophi

lised

fish

sam

ples

wer

e in

goo

d ag

reem

ent

with

tho

se o

btai

ned

by a

slu

rry

tech

niqu

e37

Bot

anic

alsa

mpl

esA

s, S

eC

EM

MD

S-20

00H

2O

–HN

O3–H

2O

2PT

FE b

omb

dige

stio

n fo

r 25

min

HG

–AA

SG

ood

resu

lts w

ere

obta

ined

for

BC

R F

D8

Mai

ze L

eave

s. S

pike

reco

veri

es o

f 95

and

105

% w

ere

obta

ined

for

As

and

Se,

resp

ectiv

ely

38

Bot

anic

alsa

mpl

esA

l, C

a, C

u,

Cr,

Fe,

K,

Mg,

Mn,

Si,

Ti,

Zn

CE

M M

DS-

81D

Tef

lon

PFA

bom

b di

gest

ion

with

(a)

HN

O3–H

Cl,

(b)

HN

O3–H

F–H

2O

2

FAA

S an

d D

CP-

AE

S (f

orC

u)(a

) G

ood

Ca,

K, M

g, M

n an

d Z

n re

sults

wer

e ob

tain

ed f

or N

IST

Citr

us L

eave

s, P

ine

Nee

dles

and

IA

EA

Mix

ed D

iet,

but

thos

efo

r Al,

Cu

and

Fe w

ere

low

. (b)

Goo

d re

sults

wer

e ob

tain

ed fo

rA

l, Fe

and

Mg

in C

itrus

Lea

ves,

but

Cu

resu

lts w

ere

slig

htly

low

39

Bio

-mon

itors

Ca,

Cd,

Cr,

Cu,

Fe, K

, Mg,

Mn,

Ni,

Pb,

Zn

CE

M M

DS-

2000

HN

O3–H

2O

2PF

A b

omb

dige

stio

n fo

r 15

min

(m

oss

and

rye

gras

s) a

nd 1

7 m

in (

hum

usan

d ha

y) (

n=

10)

FAA

S an

d E

TA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or B

CR

281

Rye

Gra

ss a

nd I

AE

AV

-10

Hay

, ex

cept

for

low

Fe

reco

veri

es.

Mos

s an

d hu

mus

sam

ples

wer

e al

so s

ucce

ssfu

lly d

iges

ted

40

Bot

anic

alsa

mpl

esC

a, C

u, F

e, K

,M

n, M

g, N

a,P,

Zn

CE

M M

DS-

81D

PTFE

bom

b di

gest

ion

for

60 m

in(n

=12

) w

ith (

a) H

NO

3an

d(b

) H

NO

3–H

2O

2

AA

S an

d A

ES

(for

Na

and

K)

No

sign

ific

ant d

iffe

renc

e w

as o

bser

ved

betw

een

the

resu

lts o

f the

two

mic

row

ave

proc

edur

es,

a co

nven

tiona

l dr

y as

hing

and

aw

et a

shin

g te

chni

que

for

luce

rne

leav

es

41

Bot

anic

alsa

mpl

esB

a, C

a, C

u,M

g, M

n, Z

nC

EM

MD

S-81

with

IR

prob

e H

NO

3–H

F PT

FE b

omb

dige

stio

nfo

r 20

min

(n

=6)

ICP

spec

trom

etry

Goo

d re

sults

wer

e ob

tain

ed f

or N

BS

Citr

us L

eave

s, e

xcep

t fo

rsl

ight

ly l

ow C

u42

Analyst, July 1998, Vol. 123 107R

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Food

sam

ples

N

a C

EM

M

DS-

2000

PTFE

bom

b H

NO

3–H

2O

2

dige

stio

n fo

r 1.

5 h

(n=

12)

AA

S, C

IE a

nd I

C a

naly

sis

No

CR

Ms

wer

e an

alys

ed43

Sew

age

slud

geA

g, A

l, B

a, B

e,C

a, C

d, C

o,C

r, C

u, F

e,K

, Mg,

Mn,

Mo,

Na,

Ni,

P, P

b, S

n,T

i, V

, Zn

CE

M M

DS-

81D

Clo

sed

vess

el H

NO

3–5

0% H

Cl

dige

stio

n fo

r 20

min

ICP-

AE

SR

esul

ts w

ere

pres

ente

d fo

r th

e ac

id l

each

able

met

als

in N

IST

SRM

278

1 D

omes

tic S

ludg

e an

d us

ed t

o de

rive

ref

eren

ceva

lues

for

the

sam

ple.

Gen

eral

ly r

esul

ts c

ompa

red

wel

l w

ithth

ose

of a

n op

en v

esse

l ho

t-pl

ate

dige

stio

n m

etho

d. S

pike

reco

veri

es o

f 89

–120

% w

ere

obta

ined

for

the

mic

row

ave

met

hod

44

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

BC

EM

MD

S-81

DH

2O

2–H

NO

3T

eflo

n bo

mb

dige

stio

n fo

r 10

min

, fol

low

ing

havi

ng l

eft

sam

ples

to

pre-

dige

st a

t ro

om t

empe

ratu

re f

or10

min

ICP-

MS

Gen

eral

ly g

ood

resu

lts w

ere

obta

ined

for

B i

n N

IST

SR

M 1

515

App

le L

eave

s, S

RM

154

7 Pe

ach

Lea

ves,

RM

843

3 C

orn

Bra

nan

d R

M 8

414

Bov

ine

Mus

cle.

Spi

ke r

ecov

erie

s of

90–

109%

wer

e ob

tain

ed

45

Bot

anic

alsa

mpl

esA

s, B

a, C

d,C

o, C

r, C

u,H

g, M

n, N

i,Pb

, Sb,

Tl,

V, Z

n

CE

M M

DS-

81D

HN

O3

Tef

lon

bom

b di

gest

ion

(18

min

) fo

llow

ed b

y 21

min

heat

ing

with

HF.

H2O

2is

the

nad

ded

and

heat

ing

cont

inue

d in

a w

ater

-bat

h (1

5 m

in)

befo

read

ding

H3B

O3

for

a fu

rthe

r5–

10 m

in h

eatin

g (n

=12

)

AA

S an

d IC

P-A

ES

Rea

sona

ble

agre

emen

t w

ith t

he c

ertif

ied

valu

es f

or N

IST

SR

M15

47 P

each

Lea

ves

was

obt

aine

d, e

xcep

t fo

r lo

w B

a. T

hem

etho

d w

as a

lso

used

to

dige

st c

orn

leav

es

46

Bot

anic

alsa

mpl

esM

nC

EM

MD

S-81

DH

NO

3T

eflo

n PF

A b

omb

dige

stio

n (a

) w

ithou

t pr

e-di

gest

ion;

(b)

with

pre

-di

gest

ion

at r

oom

tem

pera

ture

(18

h);

(c)

with

mic

row

ave

pre-

dige

stio

n an

d re

flux

(7

min

);(d

) w

ith m

icro

wav

e pr

e-di

gest

ion

with

out

refl

ux

FAA

SN

o si

gnif

ican

t di

ffer

ence

s w

ere

obse

rved

bet

wee

n th

e re

sults

obta

ined

for s

wee

t bay

pow

der b

y ea

ch o

f pro

cedu

res

(a) t

o (d

).Pr

oced

ure

(c)

perm

its a

fas

t, sa

fe d

iges

tion

with

out

larg

eev

apor

atio

n of

aci

ds i

n th

e pr

e-di

gest

ion

step

47

Food

sam

ples

Dec

ompo

-si

tion

prod

ucts

CE

M M

DS-

81D

Bom

b di

gest

ion

with

HN

O3,

HN

O3–H

2O

2or

HN

O3

follo

wed

by

H2O

2–H

ClO

4

trea

tmen

t on

a h

ot-p

late

.

Car

bon

cont

ent

anal

ysis

,IR

, TL

CR

esul

ts i

llust

rate

d th

e ne

cess

ity o

f em

ploy

ing

diff

eren

t sa

mpl

ede

com

posi

tion

met

hods

acc

ordi

ng t

o th

e sa

mpl

e m

atri

x an

dan

alyt

ical

tec

hniq

ue o

f ch

oice

48

Bot

anic

alsa

mpl

esA

s, B

, Ba,

Be,

Bi,

Ca,

Cd,

Co,

Cu,

Cr,

K, L

a, M

g,M

n, M

o, N

a,N

i, P,

Pb,

S,

Se, S

r, T

e,Z

n

CE

M M

DS-

2100

Aft

er a

ddin

g H

NO

3sa

mpl

es a

real

low

ed t

o st

and

for

35–4

0m

in, h

eate

d at

80

°C w

ith a

heat

lam

p (1

h),

coo

led

and

capp

ed. M

icro

wav

e en

ergy

is

appl

ied

in t

hree

ste

ps (

tota

l3.

5h,

n=

5) w

ith c

oolin

g an

dve

ntin

g be

twee

n st

eps.

Aft

erco

olin

g sa

mpl

es a

re e

vapo

rate

dat

80

°C u

nder

N2

purg

e fo

r4

h

ICP-

AE

SG

ener

ally

goo

d re

sults

wer

e ob

tain

ed f

or N

IST

SR

M 1

547

Peac

hL

eave

s, 1

571

Orc

hard

Lea

ves

and

1572

Citr

us L

eave

s49

Bio

logi

cal

tissu

esC

a, C

u, F

e, K

,M

g, M

n, P

S,Z

n

CE

M M

DS-

81D

Aft

er i

nitia

l cl

osed

hea

ting

with

HN

O3–H

2O

2th

e di

gest

ion

isal

low

ed t

o co

ntin

uesp

onta

neou

sly

with

out

furt

her

irra

diat

ion

ICP-

AE

S an

d FA

AS

Goo

d re

cove

ries

wer

e ob

tain

ed f

or C

a, F

e, K

, Mg,

Mn

and

S in

NIS

T B

ovin

e L

iver

. P, Z

n an

d C

u re

sults

wer

e ju

st o

utsi

de th

ece

rtif

ied

rang

e. T

he h

eatin

g tim

e re

quir

ed d

epen

ded

on t

hesa

mpl

e si

ze a

nd a

mou

nt o

f H

2O

2us

ed

50

108R Analyst, July 1998, Vol. 123

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Slud

ge s

ampl

esA

s, S

eC

EM

M

DS-

81D

PFA

bom

b di

gest

ion

for

1–2

hw

ith (

a) H

NO

3–H

Cl,

(b)

H2O

2–H

Cl–

H2SO

4,

(c)

H2O

2–H

2SO

4,

(d)

HN

O3–H

2SO

4

FI–H

G–A

AS

Met

hod

(d)

gave

the

bes

t re

cove

ries

(va

lidat

ed u

sing

NIS

T S

anJo

aqui

n So

il, s

ee T

able

2).

Goo

d re

sults

wer

e ob

tain

ed f

or A

s,bu

t Se

rec

over

ies

wer

e sl

ight

ly h

igh.

For

NIS

T D

omes

ticSe

wag

e Sl

udge

re

sults

ag

reed

w

ell

with

th

ose

of

aco

nven

tiona

l re

flux

met

hod,

but

the

mic

row

ave

met

hod

was

fast

er a

nd H

ClO

4w

as n

ot r

equi

red

51

Mar

ine

biol

ogic

altis

sues

As,

Cd,

Pb

CE

M

MD

S-20

00H

NO

3T

eflo

n PF

A b

omb

dige

stio

n fo

r up

to

2 h

depe

ndin

g on

the

sam

ple

(n=

12)

ICP-

AE

S an

d IC

P-M

SG

ood

resu

lts

wer

e ob

tain

ed

for

NR

CC

T

OR

T-1

L

obst

erH

epat

opan

crea

s an

d D

OR

M-1

Dog

fish

Mus

cle,

exc

ept

for

high

As

in t

he f

orm

er.

Spik

e re

cove

ries

wer

e in

the

ran

ge75

–117

%.

52

Bot

anic

alsa

mpl

esC

a, F

e, K

, Mg,

Mn,

P, S

CE

M M

DS-

2000

Clo

sed

dige

stio

n w

ith(a

) H

NO

3–H

ClO

4fo

r 1

h 23

min

,(b

) H

NO

3–H

2O

2

ICP

spec

trom

etry

Gen

eral

ly g

ood

resu

lts w

ere

obta

ined

for

NIE

S C

itrus

Lea

ves,

Pine

Nee

dles

and

Cor

n L

eave

s53

Mar

ine

biol

ogic

altis

sues

Ag,

As,

Cd,

Cr,

Cu,

Ni,

Pb, Z

n

CE

M S

pect

roPr

ep s

yste

man

d Fl

oyd

RM

S-15

0O

n-lin

e: 0

.5%

m/v

slu

rrie

s w

ere

dige

sted

in

20%

HN

O3–3

%H

2O

2. B

atch

: T

eflo

n bo

mb

HN

O3–H

F di

gest

ion

for

70m

in w

ith c

oolin

g st

ep h

alf

way

thro

ugh

ID–I

CP-

MS

(sta

ndar

dad

ditio

ns)

and

ET

AA

S(f

or A

s an

d C

r)

On-

line

syst

em:

good

res

ults

wer

e ob

tain

ed f

or N

RC

C L

UT

S-1

for

Cd,

Cu,

Ni a

nd P

b (A

g an

d Z

n w

ere

low

and

Cr

very

hig

h).

For

lobs

ter

hepa

topa

ncre

as, r

esul

ts w

ere

in a

gree

men

t with

the

clos

ed v

esse

l te

chni

que.

Slu

rrie

s of

Pac

ific

oys

ter

tissu

e w

ere

not

amen

able

to

dire

ct u

ptak

e by

the

Spe

ctro

Prep

sys

tem

unle

ss p

rior

dig

estio

n w

as u

nder

take

n

54

Bot

anic

alsa

mpl

esA

l, B

, Ba,

Ca,

Cr,

Cu,

Fe,

K, M

g, M

n,N

a, P

, S, S

r,Z

n

CE

M M

DS-

81D

HN

O3–H

F cl

osed

dig

estio

n fo

r37

min

(in

clud

ing

time

for

cool

ing

step

s) f

ollo

wed

by

open

hea

ting

with

H2O

2an

dSi

O2

for

30 m

in

ICP-

AE

SG

ener

ally

goo

d re

sults

wer

e ob

tain

ed fo

r NIS

T S

RM

151

5 A

pple

Lea

ves,

154

7 Pe

ach

Lea

ves,

157

3a T

omat

o L

eave

s an

d 15

75Pi

ne N

eedl

es

55

Bio

logi

cal

tissu

esA

lC

EM

MD

S-81

DH

NO

3–H

F di

gest

ion

for

30 m

info

llow

ed b

y co

olin

g, a

dditi

onof

H2O

2an

d H

3B

O3

and

evap

orat

ion

to d

ryne

ss f

or 3

0m

in (

n=

12)

ICP-

AE

SG

ood

resu

lts w

ere

obta

ined

for

NIS

T S

RM

156

6a O

yste

r T

issu

ean

d N

IES

1577

b B

ovin

e L

iver

. H

owev

er f

ollo

win

g di

gest

ion

with

H

NO

3–H

ClO

4an

d H

NO

3–H

2O

2lo

w

resu

lts

wer

eob

tain

ed i

n th

e fo

rmer

. Sp

ike

reco

veri

es o

f 95

–96%

wer

eob

tain

ed i

n cr

ab a

nd s

hrim

p m

eat

sam

ples

56

Bio

logi

cal

tissu

esB

CE

M M

DS-

81D

HN

O3

clos

ed d

iget

ion

for

35 m

info

llow

ed b

y co

olin

g, a

dditi

onof

H2O

2an

d ev

apor

atio

n fo

r 30

min

ICP-

AE

SSp

ike

reco

veri

es o

f 95–

100%

wer

e ob

tain

ed in

five

mea

t sam

ples

and

in N

IST

Oys

ter

Tis

sue

and

Bov

ine

Liv

er (

CR

Ms

not

cert

ifie

d fo

r B

)

57

Mar

ine

biol

ogic

altis

sues

Cd,

Pb

CE

M M

DS-

2000

HN

O3

dige

stio

n fo

r 20

–25

min

(n=

12)

ET

AA

SG

ood

resu

lts w

ere

obta

ined

for

Cd

and

Pb i

n N

RC

C D

OR

M-1

Dog

fish

Mus

cle

58

Mar

ine

biol

ogic

altis

sues

Hg

CE

M M

DS-

2000

HN

O3

PTFE

bom

b di

gest

ion

for

70 s

CV

-AA

SR

esul

ts w

ere

in g

ood

agre

emen

t with

the

cert

ifie

d va

lue

for N

IST

RM

50

Alb

acor

e T

una

and

spik

e re

cove

ries

of

99–1

02%

wer

eob

tain

ed

59

Mar

ine

biol

ogic

altis

sues

As,

Cd,

Co,

Cr,

Cu,

Hg,

Pb,

Zn

CE

M M

DS-

81D

HN

O3

Tef

lon

bom

b di

gest

ion

for

2 m

in f

ollo

wed

by

prec

once

ntra

tion

on a

Che

lex-

100

colu

mn

NA

A a

nd E

TA

AS

Goo

d re

sults

w

ere

obta

ined

fo

r N

RC

C

DO

RM

-1

Dog

fish

Mus

cle

60

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Al,

Ca,

Cu,

Fe,

K, M

g, M

n,N

a, N

i, Z

n

CE

M M

DS-

2000

Clo

sed

TM

AH

–ED

TA

amm

onia

cal

leac

hing

pro

cedu

refo

r 30

min

with

pri

or s

tirri

ngst

ep (

10 m

in)

FAA

S an

d E

TA

AS

Var

iabl

e re

sults

wer

e ob

tain

ed f

or N

IST

SR

M 1

577b

Bov

ine

Liv

er, N

IST

SR

M 1

515

App

le L

eave

s an

d N

IES

CR

M N

o. 1

Pepp

erbu

sh,

No.

3 C

hlor

ella

, N

o. 6

Mus

sel

and

No.

7 T

eaL

eave

s

61

Mar

ine

biol

ogic

altis

sues

Hg

Mile

ston

e M

LS-

1200

(120

0 W

)H

NO

3–H

2O

2bo

mb

dige

stio

n fo

r6

min

FI–C

V-A

AS

Goo

d re

sults

wer

e ob

tain

ed f

or H

g in

NR

CC

DO

RM

-1 D

ogfi

shM

uscl

e62

Analyst, July 1998, Vol. 123 109R

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Bot

anic

alsa

mpl

esL

anth

anid

esan

d ac

tinid

esM

ilest

one

ML

S-12

00H

NO

3–H

2O

2PT

FE b

omb

dige

stio

n fo

r 14

or

26 m

inde

pend

ing

on s

ampl

e si

ze

ICP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or C

e, E

u, S

m, T

b an

d 238U

in N

IST

App

le L

eave

s, b

ut th

ose

for 2

32T

h w

ere

low

. For

NIS

T O

rcha

rdL

eave

s, r

esul

ts w

ere

low

for

232T

h an

d sl

ight

ly l

ow f

or 2

38U

63

Sew

age

slud

gesa

mpl

esC

OD

Mile

ston

e M

LS-

1200

On-

line

K2C

r 2O

7–H

2SO

4

oxid

atio

n (3

min

)FI

spe

ctro

phot

omet

ric

dete

ctio

nR

esul

ts w

ere

in g

ood

agre

emen

t with

thos

e of

the

stan

dard

CO

Dm

etho

d fo

r se

wag

e sa

mpl

es64

Mar

ine

biol

ogic

altis

sues

As

Mile

ston

e M

LS-

1200

HN

O3–H

2O

2T

eflo

n bo

mb

dige

stio

n fo

r 12

.5 m

inFI

–HG

–AA

SR

ecov

erie

s of

13

± 1

0% a

nd 2

± 1

% w

ere

obta

ined

for A

s in

BC

R27

8 M

usse

l T

issu

e an

d B

CR

42

2 C

od

Mus

cle

due

toin

com

plet

e ox

idat

ion

of

orga

noar

seni

cals

. R

esul

ts

wer

eco

mpa

red

with

tho

se o

btai

ned

from

hig

h-pr

essu

re a

shin

g an

ddr

y as

hing

pro

cedu

res

65

Mar

ine

biol

ogic

altis

sues

Hg

Mile

ston

e M

EG

A-1

200

HN

O3–H

2O

2cl

osed

dig

estio

npr

oced

ure

FI–C

V-A

FSG

ood

agre

emen

t w

ith t

he c

ertif

ied

valu

e w

as o

btai

ned

for

Hg

inN

RC

C

DO

RM

-1

Dog

fish

M

uscl

e an

d D

OL

T-1

D

ogfi

shL

iver

66

Bio

logi

cal

tissu

esR

uM

ilest

one

ML

S-12

00H

NO

3–H

2O

2PT

FE b

omb

dige

stio

n of

hom

ogen

ised

sam

ples

(in

wat

er)

for

30 m

in

ET

AA

SSp

ike

reco

veri

es o

f 95

–101

% w

ere

obta

ined

for

live

r an

d ki

dney

sam

ples

, but

no

CR

Ms

wer

e an

alys

ed67

Duc

k eg

gsC

u, C

d, P

bM

ilest

one

ML

S-12

00H

NO

3–H

2O

2T

eflo

n bo

mb

dige

stio

n fo

r 10

min

FAA

SR

ecov

erie

s of

82–

101%

wer

e ob

tain

ed in

egg

alb

umen

and

yol

ksa

mpl

es.

68

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

B, C

d, C

u, F

e,M

n, P

, Pb,

Zn

Mile

ston

e M

LS-

1200

ME

GA

and

dom

estic

oven

(66

5W),

Tef

lon

bom

b di

gest

ion

with

(a)

HN

O3,(b

) H

NO

3–H

F–ho

t-pl

ate

evap

orat

ion

to d

ryne

ss–

HN

O3, (

c) H

NO

3–H

2O

2, (

d)H

NO

3–H

ClO

4

ICP-

AE

S, F

AA

S, E

TA

AS

(a)

Poor

pre

cisi

on.

Gen

eral

ly h

igh

P an

d lo

w F

e re

sults

wer

eob

tain

ed

for

Com

ite

Inte

r-In

stitu

ts

bota

nica

l re

fere

nce

mat

eria

ls. (

b) A

ccep

tabl

e pr

ecis

ion.

Fe

resu

lts w

ere

impr

oved

but m

ost s

till o

utsi

de c

ertif

ied

rang

e. (

c) a

nd (

d) m

ixed

Fe,

Cu,

Mn,

Zn

resu

lts fo

r NIS

T T

otal

Die

t, N

IES

Mus

sel,

Pepp

erbu

shan

d B

CR

Who

lem

eal

Flou

r (m

any

resu

lts t

oo h

igh)

69

Bio

logi

cal

tissu

esA

s, C

d, C

o,C

u, F

e, H

g,M

g, M

n,M

o, P

b, S

e,V

, Zn

Mile

ston

e M

LS-

1200

ME

GA

HN

O3

dige

stio

n (3

8 m

in)

in d

ual

PTFE

con

tain

ers

for

sam

ple

size

s of

35–

45 m

g (n

=20

)

ICP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or a

ll el

emen

ts s

tudi

ed i

n N

IST

Bov

ine

Liv

er. G

ood

resu

lts w

ere

also

obt

aine

d fo

r A

s in

IA

EA

MA

-A-2

Fis

h Fl

esh,

how

ever

Cd,

Cu,

Hg,

Se

and

Zn

wer

esl

ight

ly l

ow

70

Ric

e fl

our

Cd,

Cr,

Fe,

Pb

Mile

ston

e M

LS-

1200

ME

GA

Clo

sed

dige

stio

n w

ith (

a) H

NO

3

for

8 m

in, (

b) H

NO

3fo

r 8

min

.T

hen

cool

, add

HF

and

HC

lO4

and

heat

to

dryn

ess

at 1

00 °

C.

HN

O3

is t

hen

adde

d an

d th

esa

mpl

e he

ated

to

near

dry

ness

ID–I

CP-

MS

follo

win

gre

mov

al o

f th

e C

am

atri

x by

pas

sage

thro

ugh

a m

icro

colu

mn

(a)

For

the

rice

flo

ur r

efer

ence

mat

eria

ls N

IST

SR

M 1

568,

NIE

S10

a an

d K

RIS

S A

and

B,

good

Cd

resu

lts w

ere

obta

ined

.H

owev

er, F

e an

d C

r w

ere

low

.(b

) G

ood

resu

lts w

ere

obta

ined

for

Cr

and

Fe i

n th

e ab

ove

sam

ples

.

71

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Ca,

Cu,

Fe,

K,

Mg,

Mn,

Na,

P, Z

n

Mile

ston

e M

LS-

1200

HN

O3–H

2O

2PT

FE b

omb

dige

stio

nIC

P-A

ES

and

AA

SFo

r N

BS

Orc

hard

Lea

ves,

Bov

ine

Liv

er a

nd S

pina

ch lo

w F

e bu

tgo

od C

u, M

n, N

a, P

and

Zn

resu

lts w

ere

obta

ined

. Som

e C

a, K

and

Mg

reco

veri

es w

ere

slig

htly

low

72

Alm

ond

kern

els

Ca,

Cu,

Fe,

K,

Mg,

Mn,

Na,

P, S

, Zn

Mile

ston

e M

LS-

1200

ME

GA

HN

O3–H

2O

2T

eflo

n bo

mb

dige

stio

n fo

r 22

min

(n

=6)

ICP-

AE

ST

he e

lem

enta

l com

posi

tion

of th

e ke

rnel

s of

19

alm

ond

culti

vars

from

di

ffer

ent

orig

ins

was

de

term

ined

to

in

vest

igat

e th

ein

flue

nce

of t

he c

ultiv

ar o

n th

e m

iner

al c

ompo

sitio

n of

the

sam

ple

73

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

Al

Mile

ston

e M

LS-

1200

Tef

lon

bom

b H

NO

3–H

2O

2

dige

stio

n fo

r 23

min

(n

=3)

ET

AA

SG

ood

resu

lts w

ere

obta

ined

for

NIS

T W

heat

Flo

ur, b

ut th

ose

for

Ric

e Fl

our

wer

e sl

ight

ly h

igh.

Rea

sona

ble

agre

emen

t with

the

info

rmat

iona

l val

ues

for T

otal

Die

t and

IAE

A F

ish

Tis

sue

wer

eob

tain

ed. T

he a

dditi

on o

f H

F to

the

dige

stio

n di

d no

t inc

reas

ere

cove

ries

74

110R Analyst, July 1998, Vol. 123

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Mar

ine

biol

ogic

alsa

mpl

es

SiFl

oyd

RM

S 15

0 (8

50 W

)H

NO

3–H

2O

2–H

F T

eflo

n bo

mb

dige

stio

n fo

r 30

min

, aft

erha

ving

lef

t sa

mpl

es t

opr

edig

est

over

nigh

t. H

F is

neut

ralis

ed w

ith H

3B

O3

A t

ertia

ry a

min

e m

ixtu

reis

add

ed b

efor

e IC

P-A

ES

anal

ysis

Goo

d re

sults

wer

e ob

tain

ed fo

r NIS

T 1

566

Oys

ter T

issu

e. R

esul

tsw

ere

also

in

acce

ptab

le a

gree

men

t w

ith t

hose

obt

aine

d by

aL

iBO

2fu

sion

pro

cedu

re f

or a

ran

ge o

f fo

od s

ampl

es

75

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

As

Floy

d R

MS

150

HN

O3–H

2O

2bo

mb

dige

stio

n fo

r32

min

(n

=6)

ICP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

Oys

ter

Tis

sue

and

Orc

hard

Lea

ves

76

Mar

ine

biol

ogic

altis

sues

Ag,

Al,

As,

Cd,

Cr,

Co,

Cu,

Fe,

Hg,

Mn,

Ni,

Pb,

Se, S

n, T

h,Z

n

Floy

dH

NO

3–H

F di

gest

ion

for

42 m

in,

follo

wed

by

cool

ing,

re-

heat

ing

for

42 m

in, e

vapo

ratio

n to

dryn

ess

on a

hot

-pla

te (

with

/w

ithou

t H

2O

2)

and

re-

diss

olut

ion

in H

NO

3/H

2O

ID–I

CP-

MS

and

ICP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or A

g, A

l, A

s, C

d, C

o, C

r, C

u, F

e,H

g, M

n, N

i, Pb

, Se,

Sn,

Th

and

Zn

in N

RC

C D

OR

M-2

Dog

fish

Mus

cle

and

DO

LT

-2 D

ogfi

sh L

iver

77

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

Ca,

Cu,

Fe,

Zn

Floy

d R

MS-

150

21 d

iffe

rent

dig

estio

n pr

oced

ures

usin

g H

Cl–

HN

O3–H

F in

diff

eren

t ra

tios

DC

P-A

ES

The

mos

t su

itabl

e pr

oced

ure

was

cho

sen

by f

ract

iona

l fa

ctor

ial

desi

gn.

For

this

pro

cedu

re,

good

res

ults

wer

e ob

tain

ed f

orN

RC

C

TO

RT

-1

Lob

ster

H

epat

opan

crea

s an

d N

IST

Pi

neN

eedl

es (

Ca

and

Fe o

nly)

. Spi

ke r

ecov

erie

s of

96–

105%

wer

eob

tain

ed.

A d

etri

men

tal

effe

ct o

f aq

ua r

egia

was

rep

orte

d(H

NO

3an

d H

Cl

mos

t ef

fect

ive

in e

qual

qua

ntiti

es)

78

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

As,

Cd,

Co,

Cu,

Ni,

PbPM

D, P

aar

(Gra

z,A

ustr

ia)

Qua

rtz

tube

clo

sed

HN

O3–H

ClO

4

dige

stio

n (p

roce

dure

is

depe

nden

t on

the

sam

ple)

DP-

ASV

and

HG

–AA

S(f

or A

s)M

ixed

res

ults

wer

e ob

tain

ed f

or C

d, C

u an

d Pb

in

BC

R B

ovin

ean

d C

od M

uscl

e, B

ovin

e L

iver

, M

usse

l T

issu

e an

d B

row

nB

read

. R

esul

ts

for

Co

in

NR

CC

T

OR

T-1

L

obst

erH

epat

opan

crea

s w

ere

good

but

wer

e sl

ight

ly l

ow f

or N

i. Fo

rth

e de

term

inat

ion

of A

s in

fis

h an

d co

okin

g oi

l (by

HG

–AA

S)ad

ditio

n of

H2SO

4w

as n

eede

d. G

ood

As

resu

lts w

ere

obta

ined

for

BC

R C

od M

uscl

e, M

usse

l T

issu

e, N

IST

Orc

hard

Lea

ves

and

for

NR

CC

TO

RT

-1 L

obst

er H

epat

opan

crea

s

79

Bot

anic

alsa

mpl

esA

l, A

s, B

, Ba,

Ca,

Cd,

Co,

Cr,

Cu,

Fe,

K, L

i, M

g,M

n, M

o, N

i,Pb

, Sb,

Se,

Sr, T

i, T

l,T

h, U

, V, Z

n

Que

stro

n (M

erce

rvill

e, N

J,U

SA)

Q-W

ave

1000

HN

O3

PFA

bom

b di

gest

ion

for

30 m

in, a

fter

lea

ving

sam

ples

to p

re-d

iges

t ov

erni

ght

(n=

12)

ICP-

MS

Rea

sona

ble

agre

emen

t with

the

cert

ifie

d va

lues

was

obt

aine

d fo

rN

IST

SR

M 1

515

App

le L

eave

s an

d 15

47 P

each

Lea

ves,

alth

ough

som

e re

sults

wer

e to

o hi

gh a

nd s

ome

too

low

80

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Ni

Dom

estic

ove

n (7

00W

)H

NO

3–H

Cl

PTFE

bom

b di

gest

ion

for

14 m

in (

n=

3)IC

P-A

ES

anal

ysis

aft

erex

trac

tion

of N

ico

mpl

ex f

orm

ed w

ithD

PTH

int

o bu

tan-

1-ol

Gen

eral

ly g

ood

agre

emen

t w

ith c

ertif

ied

valu

es f

or B

CR

Oliv

eE

urop

ea,

Lag

aros

ipho

n M

ajor

, Pl

atih

pnid

ium

Rip

ario

dide

s;N

RC

C D

OR

M-1

Dog

fish

Mus

cle,

DO

LT

-1 D

ogfi

sh L

iver

,T

OR

T-1

Lob

ster

Hep

atop

ancr

eas;

NIS

T C

itrus

Lea

ves;

BC

RPi

g K

idne

y an

d B

ovin

e M

uscl

e

81

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

Ni

Dom

estic

ove

n(7

00 W

)H

NO

3–H

Cl

PTFE

bom

b di

gest

ion

for

14 m

in (

n=

3)IC

P-A

ES

anal

ysis

aft

erex

trac

tion

of N

ico

mpl

ex f

orm

ed w

ithB

PTH

int

o IB

MK

Goo

d ag

reem

ent w

ith th

e ce

rtif

ied

valu

es w

as o

btai

ned

for

NIS

TC

itrus

Lea

ves,

NR

CC

DO

RM

-1 D

ogfi

sh M

uscl

e an

d N

RC

CT

OR

T-1

Lob

ster

Hep

atop

ancr

eas

82

Mar

ine

biol

ogic

altis

sues

Al

Dom

estic

ove

n (8

00 W

)O

n-lin

e H

NO

3di

gest

ion

ofsl

urri

es (

in 0

.2%

HN

O3)

Off

-lin

e an

alys

is b

yE

TA

AS

90%

rec

over

y fo

r A

l in

NIS

T S

RM

156

6a O

yste

r T

issu

e w

asob

tain

ed. F

ive

fres

h sh

ellf

ish

sam

ples

wer

e al

so a

naly

sed

83

Analyst, July 1998, Vol. 123 111R

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Mar

ine

biol

ogic

altis

sues

SeD

omes

tic o

ven

(800

W)

On-

line

dige

stio

n of

slu

rrie

s (i

n0.

2% H

NO

3)

for

4 m

in(s

topp

ed f

low

)

Off

-lin

e an

alys

is b

yE

TA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

SR

M 1

566a

Oys

ter

Tis

sue.

No

sign

ific

ant

diff

eren

ces

wer

e ob

serv

ed b

etw

een

the

resu

ltsob

tain

ed f

or l

yoph

ilise

d an

d un

lyop

hilis

ed s

ampl

es

84

Bot

anic

alsa

mpl

esH

gD

omes

tic o

ven

(800

W)

HN

O3

PTFE

bom

b di

gest

ion

for

3 m

in a

t 80

0 W

(n

=5)

FAN

ES

afte

r re

duct

ion

with

SnC

l 2an

d in

sit

upr

econ

cent

ratio

n

Goo

d ag

reem

ent w

ith c

ertif

ied

valu

es fo

r NIS

T C

itrus

Lea

ves

and

Pine

Nee

dles

was

obt

aine

d85

Sew

age

slud

geC

d, C

r, C

u, N

i,Pb

, Zn

Dom

estic

ove

n (6

62 W

)O

n-lin

e di

gest

ion

of 0

.2–0

.75%

m/v

slu

rrie

s pr

epar

ed i

n 1.

5 m

HN

O3.

On-

line

ICP-

AE

S an

alys

isG

ener

ally

goo

d re

sults

wer

e ob

tain

ed f

or B

CR

Sew

age

Slud

geIn

dust

rial

86

Bio

logi

cal

tissu

esC

u, F

e, Z

nD

omes

tic o

ven

(700

W)

HN

O3–H

2O

2op

en d

iges

tion

for

14 m

in (

n=

100)

FI–A

AS

Goo

d re

sults

wer

e ob

tain

ed f

or C

u, F

e an

d Z

n in

NB

S B

ovin

eL

iver

and

for

Zn

in B

CR

Bov

ine

Mus

cle,

alth

ough

res

ults

for

Fe a

nd C

u w

ere

just

out

side

the

cer

tifie

d ra

nge

87

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

PbD

omes

tic o

ven

(700

W)

On-

line

HC

l–H

NO

3di

gest

ion

ofsa

mpl

es (

disp

erse

d in

Tri

ton

X-

100

solu

tion)

On-

line

anal

ysis

by

FI–

ET

AA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or B

CR

Bov

ine

Mus

cle,

Pig

Kid

ney

and

NIS

T B

ovin

e L

iver

. Fo

r N

IST

Pin

es N

eedl

es a

nd B

CR

Ole

a E

urop

ea r

esul

ts w

ere

slig

htly

low

88

Frui

t sl

urri

esan

d ju

ices

PbD

omes

tic o

ven

(650

W)

On-

line

HN

O3

dige

stio

n of

liq

uid

and

slur

ried

sam

ples

(di

sper

sed

in T

rito

n X

-100

)

On-

line

anal

ysis

by

FI–

HG

–AA

SN

o si

gnif

ican

t dif

fere

nces

wer

e ob

serv

ed f

or th

e re

sults

obt

aine

dby

FI–

MW

–HG

–AA

S an

d a

conv

entio

nal

Al

heat

ing

bloc

kdi

gest

ion

(ET

AA

S an

alys

is)

89

Food

and

fee

dcr

ops

PbD

omes

tic o

ven

(600

W)

HN

O3

PTFE

bom

b di

gest

ion

with

V2O

5ca

taly

st f

or 9

0 s

ET

AA

SG

ood

resu

lts w

ere

obta

ined

for

NIS

T C

itrus

Lea

ves

90

Frui

t sl

urri

esC

d, C

u, F

e, P

b,Se

Dom

estic

ove

n (6

00W

)H

NO

3PT

FE b

omb

dige

stio

n w

ithV

2O

5ca

taly

st f

or 9

0 s

ET

AA

SR

esul

ts w

ere

in g

ood

agre

emen

t w

ith t

hose

obt

aine

d by

a s

lurr

ypr

oced

ure

91

Mar

ine

biol

ogic

altis

sues

Hg

Dom

estic

ove

n (7

00 W

)H

NO

3PT

FE b

omb

dige

stio

n fo

r20

min

aft

er l

eavi

ng s

ampl

esov

erni

ght

to p

artia

lly d

iges

t(n

=10

)

CV

-AFS

, IC

P-M

S an

dID

–IC

P-M

SR

esul

ts o

btai

ned

afte

r an

alys

is b

y C

V-A

FS,

ICP-

MS

(sta

ndar

dad

ditio

ns)

and

ID–I

CP-

MS

(spi

ke a

dded

pri

or t

o ov

erni

ght

dige

stio

n) w

ere

in g

ood

agre

emen

t with

the

cert

ifie

d va

lues

for

BC

R C

od M

uscl

e

92

Bot

anic

al a

ndse

wag

esl

udge

sam

ples

Cu,

Mn

Dom

estic

ove

n (6

50W

)O

n-lin

e di

gest

ion

of H

NO

3–H

2O

2

slur

ries

for

2 m

in (

bota

nica

l)an

d 4

min

(se

wag

e sl

udge

)

On-

line

anal

ysis

by

FAA

SG

ood

resu

lts w

ere

obta

ined

for

Mn

in N

IST

Tom

ato

Lea

ves.

For

CB

R S

ewag

e Sl

udge

–Dom

estic

and

Ind

ustr

ial

resu

lts w

ere

gene

rally

in

good

agr

eem

ent

with

the

cer

tifie

d va

lues

93

Bot

anic

alsa

mpl

esC

o, C

r, N

iD

omes

tic o

ven

(800

W)

On-

line

mic

row

ave

dige

stio

n of

slur

ries

pre

pare

d in

5%

HN

O3

Off

-lin

e an

alys

is b

yE

TA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or C

r an

d N

i in

NIS

T C

itrus

Lea

ves.

Res

ults

for C

o, C

r and

Ni i

n ve

geta

ble

sam

ples

wer

e co

mpa

red

with

tho

se o

btai

ned

by d

irec

t sl

urry

ana

lysi

s an

d by

a d

ryas

hing

met

hod

94

Bot

anic

al a

ndse

wag

esl

udge

sam

ples

Cr

Dom

estic

ove

n (6

50 W

)A

qua

regi

a–H

2O

2PT

FE b

omb

dige

stio

nE

TA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or C

r in

NIS

T T

omat

o L

eave

s an

dC

itrus

L

eave

s.

Res

ults

w

ere

also

in

ag

reem

ent

with

th

ein

form

atio

nal v

alue

for

BC

R S

ewag

e Sl

udge

. Spi

ke r

ecov

erie

sof

98–

103%

wer

e ob

tain

ed

95

Bio

logi

cal

tissu

es a

ndse

wag

esl

udge

sam

ples

Cd

Dom

estic

ove

n (6

50 W

)B

iolo

gica

l: cl

osed

ves

sel

HN

O3

(14

m)–

H2O

2di

gest

ion

(12.

5m

in)

Slud

ge:

clos

ed v

esse

laq

ua r

egia

–HF–

H2O

2di

gest

ion

follo

wed

by

H3B

O3

trea

tmen

t

ET

AA

SG

ood

resu

lts w

ere

obta

ined

for

BC

R P

ig K

idne

y, B

CR

Sew

age

Slud

ge

Dom

estic

an

d fo

r M

A-M

-2/T

M

Mus

sel

Tis

sue

(IA

EA

)

96

Mar

ine

biol

ogic

al,

bota

nica

lan

d se

wag

esl

udge

sam

ples

Ni

Dom

estic

ove

n (1

100

W)

Aqu

a re

gia–

HF–

H2O

2PT

FEbo

mb

dige

stio

n fo

r 12

min

(4

step

s) w

ith c

oolin

g be

twee

nea

ch s

tep.

Aft

er a

ddin

g H

3B

O3

the

sam

ple

is h

eate

d in

abo

iling

wat

er b

ath

for

10 m

in

ET

AA

SG

ood

resu

lts w

ere

obta

ined

for

Ni

in N

IES

No.

10c

Ric

e Fl

our

(unp

olis

hed)

, IA

EA

No.

325

Mus

sel T

issu

e, B

CR

CR

M 1

43R

Sew

age

Slud

ge A

men

ded

Soil

and

in C

RM

144

Dom

estic

Sew

age

Slud

ge

97

112R Analyst, July 1998, Vol. 123

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Bot

anic

al a

ndse

wag

esl

udge

sam

ples

Cu,

Mn,

Pb,

Zn

Dom

estic

ove

n (6

50 W

)Sl

urri

es (

prep

ared

in

HN

O3)

are

mer

ged

on-l

ine

with

H2O

2an

ddi

gest

ed a

t 10

0% p

ower

On-

line

FAA

SR

esul

ts w

ere

in g

ood

agre

emen

t with

the

cert

ifie

d va

lue

for M

n in

NIS

T T

omat

o L

eave

s, f

or C

u, M

n an

d Pb

in

CB

R S

ewag

eSl

udge

–Ind

ustr

ial

and

for

Pb i

n Se

wag

e Sl

udge

–Dom

estic

.R

esul

ts w

ere

poor

for C

u an

d M

n in

Sew

age

Slud

ge–D

omes

tican

d fo

r Z

n in

bot

h se

wag

e C

RM

s

98

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

BD

omes

tic o

ven

HN

O3–H

2O

2PT

FE b

omb

dige

stio

n fo

r 1

h (n

=2)

Phot

omet

ry, f

luor

imet

ry,

ICP-

MS

and

ICP-

AE

SG

ood

resu

lts w

ere

obta

ined

for

NB

S T

omat

o L

eave

s an

d Pi

neN

eedl

es, a

lthou

gh r

ecov

erie

s fo

r B

ovin

e L

iver

wer

e lo

w99

Mar

ine

biol

ogic

altis

sues

Cd

Dom

estic

ove

nC

lose

d di

gest

ion

for

135

s(n

=6)

with

(a)

HN

O3, (

b)H

2SO

4an

d (c

) H

NO

3–H

2SO

4.

Aft

er c

oolin

g H

2O

2is

add

ed,

but

no h

eatin

g is

app

lied

FAA

SSp

ike

reco

veri

es o

f (a

) 95

–107

%,

(b)

60–7

1% a

nd (

c) 7

3–89

%w

ere

obta

ined

. Dig

estio

n (a

) w

as c

hose

n fo

r fu

rthe

r st

udy

and

used

to

di

gest

N

IST

SR

M

1566

a O

yste

r T

issu

e.

Goo

dag

reem

ent

with

the

cer

tifie

d va

lue

for

Cd

was

obt

aine

d

100

Bot

anic

alsa

mpl

esC

a, C

o, C

r, C

u,Fe

, K, M

g,M

n, N

i, Pb

,Z

n

Dom

estic

ove

n (5

50W

)H

NO

3–H

2O

2T

eflo

n bo

mb

dige

stio

n w

ith w

ater

coo

led

spir

al f

or 6

min

(n

=1)

FAA

S an

d FA

ES

Goo

d re

sults

wer

e ob

tain

ed f

or C

o an

d C

r in

ISS

/MM

M c

ertif

ied

Gre

en A

lgae

. Pb

and

Ni

resu

lts w

ere

just

out

side

the

cer

tifie

dra

nge.

Acc

epta

ble

resu

lts w

ere

obta

ined

for

the

‘in

-hou

se’

refe

renc

e m

ater

ial

Luc

erne

, exc

ept

for

Fe a

nd Z

n

101

Oct

ocor

als

Cd,

Cu,

Ni

Pb,

Zn

Dom

estic

ove

n (6

00 W

)M

icro

wav

e pr

e-dr

ying

(20

–50

min

) fo

llow

ed b

y H

NO

3

dige

stio

n in

pyr

ex t

ubes

for

1m

in (

4–6

times

) w

ith c

oolin

gbe

twee

n st

eps

ET

AA

S an

d FA

AS

(for

Zn)

Goo

d re

cove

ries

wer

e ob

tain

ed f

or a

syn

thet

ic C

RM

pre

pare

dfr

om a

mix

ture

of

61%

NIE

S M

usse

l an

d 39

% C

aCO

3. E

ight

octo

cora

l sp

ecie

s w

ere

also

ana

lyse

d

102

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Ca,

Cu,

Fe,

Mg,

Mn,

Zn

Dom

estic

ove

n (5

00 W

)H

NO

3–H

ClO

4–H

Cl–

HF

PTFE

bom

b di

gest

ion

(with

poly

prop

ylen

e ja

cket

) fo

r 14

min

(n

=6)

‘One

-dro

p’ F

AA

SR

esul

ts w

ere

in g

ood

agre

emen

t w

ith t

he c

ertif

ied

valu

es f

orN

IST

Bov

ine

Liv

er,

NIE

S Pe

pper

bush

and

Mus

sel

sam

ples

.Fo

r N

IES

Tea

Lea

ves,

Fe

resu

lts w

ere

high

and

Ca

low

. C

are

sults

wer

e al

so l

ow f

or N

IES

Sarg

asso

103

Bot

anic

alsa

mpl

esC

dD

omes

tic o

ven

HN

O3–H

ClO

4–H

Cl–

HF

PTFE

bom

b di

gest

ion

(with

poly

prop

ylen

e ja

cket

) fo

r 9

min

(n

=6)

, fol

low

ed b

y ho

t-pl

ate

evap

orat

ion

to d

ryne

ssan

d di

ssol

utio

n in

HC

lO4

Fe w

as r

emov

ed w

ithH

IPT

in

benz

ene

and

the

Cd

com

plex

for

med

with

APD

C w

asex

trac

ted

into

chlo

rofo

rm f

or ‘

one-

drop

’ FA

AS

anal

ysis

Res

ults

wer

e in

goo

d ag

reem

ent

with

the

cer

tifie

d va

lues

for

NIE

S Pe

pper

bush

and

Ric

e Fl

our

(low

and

med

ium

) an

d fo

rN

IST

Pin

e N

eedl

es, O

rcha

rd a

nd C

itrus

Lea

ves

104

Mar

ine

biol

ogic

altis

sues

SeD

omes

tic o

ven

(600

W)

HN

O3–H

2SO

4–H

2O

2PT

FE b

omb

dige

stio

nSe

VIis

red

uced

to

SeIV

.T

he c

ompl

exSe

(O)S

O322

is f

orm

edan

d an

alys

ed b

y D

PP

Res

ults

wer

e in

goo

d ag

reem

ent w

ith th

e ce

rtif

ied

valu

e fo

r Se

inN

IES

No.

6 M

usse

l sa

mpl

e10

5

Mar

ine

biol

ogic

altis

sues

SeD

omes

tic o

ven

(600

W)

PTFE

bom

b di

gest

ion

with

(a)

HN

O3–H

2O

2, (

b) H

NO

3–

H2SO

4–H

2O

2, (

c) H

NO

3–

H3PO

4–H

2O

2, (

d) H

NO

3–

K2S 2

O8–H

2O

2

SeV

Iis

red

uced

to

SeIV

for

anal

ysis

by

HG

–AA

SG

ood

resu

lts w

ere

obta

ined

for

NIE

S M

usse

l fol

low

ing

dige

stio

nby

pr

oced

ure

(b).

Pr

oced

ures

(a

),

(c)

and

(d)

gave

lo

wre

cove

ries

106

Mar

ine

biol

ogic

altis

sues

As

Dom

estic

ove

n (7

00 W

)O

n-lin

e po

tass

ium

per

sulf

ate–

NaO

H o

xida

tion,

fol

low

ing

HPL

C s

epar

atio

n of

As

spec

ies

in s

ampl

e ex

trac

ts

On-

line

anal

ysis

by

HG

–AA

SA

sV, M

MA

, DM

A, a

rsen

ocho

line

and

arse

nobe

tain

e le

vels

wer

ede

term

ined

in a

syn

thet

ic fi

sh e

xtra

ct, a

lthou

gh n

o C

RM

s w

ere

anal

ysed

. Spi

ke r

ecov

erie

s of

96–

110%

wer

e ob

tain

ed

107

Mar

ine

biol

ogic

altis

sues

As

Dom

estic

ove

n (7

50W

)Sa

mpl

e w

as h

eate

d w

ith H

Cl–

KI

in a

PT

FE b

omb

for

8 m

in(n

=1)

. The

dis

tille

d A

sCl 3

was

col

lect

ed i

nhy

drox

ylam

ine

hydr

ochl

orid

e

HG

–AA

SG

ood

spik

e re

cove

ries

wer

e ob

tain

ed f

or i

norg

anic

ars

enic

in

am

usse

l sam

ple.

How

ever

, org

anoa

rsen

ic c

ompo

unds

wer

e no

tde

com

pose

d

108

Analyst, July 1998, Vol. 123 113R

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Bot

anic

alsa

mpl

esC

a, K

, Mg,

P,

SD

omes

tic o

ven

(750

W)

HN

O3–H

ClO

4op

en d

iges

tion

for

15–3

0 m

in d

epen

ding

on

the

sam

ple

(n=

25)

ICP-

AE

S an

alys

isG

ood

resu

lts w

ere

obta

ined

for P

in N

BS

Pine

Nee

dles

and

Citr

usL

eave

s, a

lthou

gh r

esul

ts f

or C

a an

d K

in

the

form

er w

ere

slig

htly

out

side

the

cer

tifie

d ra

nge

109

Bio

logi

cal

tissu

esA

sD

omes

tic o

ven

(650

W)

HN

O3–H

2SO

4–H

2O

2PT

FE b

omb

dige

stio

nH

G–A

AS

with

a m

odif

ied

elec

tric

al h

eatin

gsy

stem

Goo

d re

sults

for A

s in

NIS

T B

ovin

e L

iver

and

spi

ke re

cove

ries

of

91–1

08%

wer

e ob

tain

ed11

0

Food

sam

ples

Bro

mid

e io

nsD

omes

tic o

ven

NaO

H (

0.5

m)

bom

b di

gest

ion

for

4 m

in. A

fter

coo

ling,

H2O

2is

adde

d an

d he

atin

g co

ntin

ued

for

a fu

rthe

r 2

min

(n

=2)

Ion-

exch

ange

chro

mat

ogra

phy

(UV

spec

trom

etri

cde

tect

ion)

, fol

low

ing

catio

n ex

chan

gere

mov

al o

f N

a

Bro

mid

e io

ns w

ere

dete

rmin

ed i

n to

tal

diet

sam

ples

. Sp

ike

reco

veri

es o

f 87

–119

% w

ere

obta

ined

in

four

dif

fere

nt f

ood

sam

ples

111

Mar

ine

biol

ogic

altis

sues

Hg

Dom

estic

ove

n (7

50 W

)H

NO

3–H

2O

2PT

FE b

omb

dige

stio

n fo

r 5

min

, aft

erle

avin

g th

e sa

mpl

e to

pre

dige

stov

erni

ght

CV

-AA

SG

ood

resu

lts w

ere

obta

ined

for

tot

al H

g in

NR

CC

DO

RM

-1D

ogfi

sh M

uscl

e. T

una

fish

sam

ples

wer

e al

so a

naly

sed

and

spik

e re

cove

ries

of

91–9

3% w

ere

obta

ined

112

Mar

ine

biol

ogic

altis

sues

As

Dom

estic

ove

n (6

00W

)H

NO

3PT

FE b

omb

dige

stio

n w

ithca

taly

st o

f V

2O

5fo

r 90

sH

G–A

AS

Res

ults

wer

e in

goo

d ag

reem

ent w

ith th

e ce

rtif

ied

valu

e fo

r B

CR

Mus

sel

Tis

sue

and

spik

e re

cove

ries

of

93

–101

%

wer

eob

tain

ed

113

Mar

ine

biol

ogic

altis

sues

Hg

Dom

estic

ove

n (6

00 W

)H

NO

3bo

mb

dige

stio

n of

sam

ples

and

stan

dard

s fo

r 90

sC

V-A

AS

Goo

d re

sults

for

BC

R M

usse

l T

issu

e an

d sp

ike

reco

veri

es o

f95

–106

% w

ere

obta

ined

114

Bot

anic

alsa

mpl

esA

sD

omes

tic o

ven

(600

W)

HN

O3

bom

b di

gest

ion

with

cata

lyst

of

V2O

5fo

r 90

sH

G–A

AS

Res

ults

wer

e in

goo

d ag

reem

ent w

ith th

e ce

rtif

ied

valu

es fo

r NB

SC

itrus

Lea

ves

115

Tot

al d

iet

sam

ples

Al,

Ca,

Cu,

Fe,

K, M

g, N

a,P,

Zn

Dom

estic

ove

n (7

50 W

)D

iges

tion

(qua

rtz

vess

el)

with

(a)

HN

O3, (

b) H

NO

3–H

2O

2, (

c)H

NO

3–H

2SO

4, (

d) H

NO

3–H

Cl

ICP-

AE

SG

ood

resu

lts w

ere

obta

ined

for

NIS

T T

otal

Die

t ex

cept

for

(a)

slig

htly

low

K a

nd Z

n, (

b) s

light

ly l

ow K

, (c

) sl

ight

ly h

igh

Pan

d sl

ight

ly l

ow K

, (d)

low

Al,

K a

nd Z

n

116

Mar

ine

biol

ogic

altis

sues

As

Dom

estic

ove

nH

NO

3T

eflo

n bo

mb

dige

stio

n fo

r90

sE

TA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

Oys

ter

Tis

sue

117

Bio

logi

cal

tissu

esSe

Dom

estic

ove

n (6

50 W

)H

NO

3T

eflo

n bo

mb

dige

stio

n (3

min

) fo

llow

ed b

y ev

apor

atio

nto

dry

ness

with

HC

lO4

(tw

ice)

and

re-d

isso

lutio

n in

H2O

SW-C

SV f

ollo

win

gre

duct

ion

of S

eVIto

SeIV

Res

ults

wer

e in

goo

d ag

reem

ent

with

the

cer

tifie

d va

lues

for

NIS

T B

ovin

e L

iver

(sa

mpl

e am

ount

5 m

g)11

8

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Ca,

Fe,

Mg,

Zn

Dom

estic

ove

n (8

00 W

)H

NO

3cl

osed

dig

estio

n fo

r 7

min

(n=

2)IC

P-A

ES

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

157

7 B

ovin

e L

iver

(ex

cept

slig

htly

hig

h M

g an

d Z

n) a

nd fo

r 157

0 Sp

inac

h (e

xcep

t slig

htly

low

Ca

and

Fe)

119

Food

sam

ples

Al

Dom

estic

ove

nH

NO

3PT

FE b

omb

dige

stio

n (3

2m

in)

ICP-

AE

SG

ener

ally

low

resu

lts w

ere

obta

ined

for t

otal

die

t sam

ples

. Hig

her

reco

veri

es

wer

e ob

tain

ed

by

a H

NO

3–H

F–H

NO

3–H

ClO

4

dige

stio

n in

a d

ryin

g ov

en

120

Bot

anic

alsa

mpl

esC

d, C

u, P

b, Z

nD

omes

tic o

ven

(850

W)

HN

O3–H

ClO

4di

gest

ion

in q

uart

zcr

ucib

le p

lace

d in

side

Tef

lon

bom

b fo

r 29

min

(n

=4)

follo

wed

by

hot-

plat

eev

apor

atio

n to

dry

ness

DP-

ASV

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

Citr

us L

eave

s, L

ucer

neP-

alfa

lfa

(Slo

vaki

a) a

nd C

L-1

Cab

bage

leav

es (P

olan

d) (e

xcep

tlo

w C

u).

Cu,

Pb

and

Zn

resu

lts w

ere

low

for

NIS

T A

pple

Lea

ves

121

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Cd,

Cu,

Pb,

Zn

Dom

estic

ove

nH

NO

3–H

ClO

4di

gest

ion

in q

uart

zcr

ucib

le p

lace

d in

side

Tef

lon

bom

b fo

r 11

min

(n

=10

)

DP-

ASV

Gen

eral

ly g

ood

resu

lts w

ere

obta

ined

for

CL

-1 C

abba

ge L

eave

s(P

olan

d), P

-alf

alfa

Luc

erne

(Sl

ovak

ia),

BC

R R

ye G

rass

, SR

MA

pple

Lea

ves,

BC

R a

nd S

RM

157

7b B

ovin

e L

iver

122

114R Analyst, July 1998, Vol. 123

Tab

le 1

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Sew

age

slud

geC

d, C

r, P

bD

omes

tic o

ven

HC

l–H

NO

3T

eflo

n bo

mb

dige

stio

n (2

0 m

in)

follo

win

gpr

e-di

gest

ion

over

nigh

t

ET

AA

SG

ood

resu

lts w

ere

obta

ined

for P

b an

d C

r in

BC

R S

ewag

e Sl

udge

(CR

M 1

45R

) bu

t C

d re

sults

wer

e sl

ight

ly l

ow12

3

Bio

logi

cal

tissu

esPo

Dom

estic

ove

n (6

50 W

)H

NO

3PF

A b

omb

dige

stio

n (1

hfo

r pl

ants

and

2 h

for

ani

mal

tissu

e, n

=4)

, fol

low

ed b

yev

apor

atio

n to

dry

ness

and

re-d

isso

lutio

n in

HC

l

Alp

ha s

pect

rom

etry

aft

erpl

atin

g on

silv

er d

iscs

A g

ood

leve

l of p

reci

sion

for r

esul

ts w

as a

chie

ved

with

no

loss

of

Po d

urin

g th

e di

gest

ion

124

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

Cd,

Co,

Cu,

Ni,

PbD

omes

tic o

ven

HN

O3–H

Cl–

HC

lO4–H

F PT

FEbo

mb

dige

stio

nIC

P-A

ES

Goo

d C

u an

d Pb

, but

low

Cd,

Co

and

Ni r

esul

ts w

ere

obta

ined

for

NIE

S Pe

pper

bush

. Res

ults

wer

e al

so g

ood

for C

d, C

u an

d Pb

inC

hlor

ella

. For

NIE

S M

usse

l, C

d, C

o an

d C

u re

sults

wer

e go

od,

how

ever

Ni

and

Pb w

ere

low

. G

ener

ally

low

res

ults

wer

eob

tain

ed f

or N

IES

Tea

Lea

ves

125

Mar

ine

biol

ogic

altis

sues

Cd,

Cu,

Pb,

Zn

Dom

estic

ove

nH

NO

3PT

FE b

omb

dige

stio

n fo

r6.

5 m

in (

n=

4)FA

AS

and

ET

AA

SG

ener

ally

goo

d re

sults

wer

e ob

tain

ed in

NR

C-D

Dog

fish

(ex

cept

low

C

u),

NR

C-E

Sc

allo

p (e

xcep

t lo

w

Cd)

an

d N

RC

-FSw

ordf

ish

(exc

ept

low

Cu)

126

Bot

anic

alsa

mpl

esC

oD

omes

tic o

ven

HN

O3–H

Cl

bom

b di

gest

ion

for

10 m

in f

ollo

wed

by

hotp

late

evap

orat

ion

to d

ryne

ss

FI–s

pect

roph

otom

etri

cde

term

inat

ion

follo

win

gco

mpl

exat

ion

with

PSA

A

Res

ults

wer

e in

goo

d ag

reem

ent

with

the

cer

tifie

d va

lues

for

NIE

S Pe

pper

bush

127

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Cd,

Cu,

Fe,

Mn,

Pb

—O

pen

HN

O3–H

2O

2-d

iges

tion,

follo

win

g ha

ving

lef

t th

esa

mpl

e to

pre

-dig

est

over

nigh

t

ET

AA

SG

ener

ally

goo

d re

sults

wer

e ob

tain

ed f

or B

CR

Bov

ine

Mus

sel,

Ole

a E

urop

ea (

exce

pt h

igh

Cu)

, L

agar

osip

houm

ajur

(ex

cept

low

Cu)

, Pi

g K

idne

y (e

xcep

t lo

w C

u, F

e, Z

n) a

nd f

or N

BS

Citr

us L

eave

s (e

xcep

t hig

h C

u), P

ine

Nee

dles

(ex

cept

low

Pb)

and

Whe

at F

lour

128

Mar

ine

biol

ogic

altis

sues

As

—H

2SO

4–H

NO

3–H

2O

2cl

osed

dige

stio

n fo

r 30

min

ICP-

AE

SA

sel

ectio

n of

fish

and

she

llfis

h sa

mpl

es w

ere

anal

ysed

; how

ever

,no

CR

MS

wer

e in

clud

ed12

9

Bot

anic

alsa

mpl

esA

l, Fe

, Si

—H

NO

3–H

2O

2–H

F di

gest

ion

for

13m

inIC

P sp

ectr

omet

ryU

CD

155

(A

voca

do);

176

(C

itrus

); 1

24 (

Bar

ley

Hul

ls)

and

190

(Ric

e St

raw

) an

d N

IST

154

7 (P

each

) sa

mpl

es w

ere

anal

ysed

130

Food

sam

ples

Am

ino

acid

s—

Hyd

roly

sis

perf

orm

ed b

y he

atin

gw

ith 6

mH

Cl

in a

clo

sed

vess

el

—T

he a

min

o ac

id s

eque

nce

obta

ined

from

mic

row

ave

dige

stio

n an

da

conv

entio

nal

met

hod

wer

e co

mpa

red

in

bovi

ne

seru

mal

bum

in a

nd D

urum

whe

at s

ampl

es

131

Bot

anic

alsa

mpl

esPh

enol

ic a

cids

—T

eflo

n bo

mb

NaO

H d

iges

tion

at70

0 W

for

90

sH

PLC

The

lib

erat

ion

of b

-eth

er b

ound

phe

nolic

aci

ds f

rom

pla

nt c

ell

wal

ls o

f m

aize

, w

heat

, oi

lsee

d ra

pe s

tem

s an

d ba

rley

was

an

orde

r of

mag

nitu

de m

ore

effe

ctiv

e th

an w

ith a

dio

xane

—H

Cl

proc

edur

e an

d as

ef

fect

ive,

bu

t fa

r qu

icke

r th

anhi

gh-t

empe

ratu

re a

lkal

ine

dige

stio

ns

132

Bot

anic

alsa

mpl

esP

—H

NO

3–H

2O

2–H

Cl

dige

stio

nIC

P-A

ES

Res

ults

wer

e in

goo

d ag

reem

ent w

ith th

e ce

rtif

ied

valu

e fo

r NIS

TC

itrus

Lea

ves

133

Bio

logi

cal

tissu

es a

ndbo

tani

cal

sam

ples

Ag,

Ba,

Cd,

Cs,

Hg,

Mo,

Pb, R

b, S

b,Sn

, Sr

—H

NO

3PT

FE b

omb

dige

stio

n fo

r40

min

ICP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or A

g, M

o, P

b an

d R

b in

NIS

TB

ovin

e L

iver

(Sr

slig

htly

hig

h),

for

Rb

in N

IST

Whe

at F

lour

(Mo

slig

htly

hig

h) a

nd f

or C

d an

d H

g in

BC

R P

ig K

idne

y

134

Mar

ine

biol

ogic

altis

sues

and

bota

nica

lsa

mpl

es

Al

—H

NO

3PT

FE b

omb

dige

stio

n w

ithse

ven

heat

ing

step

s (t

otal

56

min

), w

ith c

oolin

g be

twee

nea

ch s

tep

ET

AA

SR

esul

ts w

ere

in g

ood

agre

emen

t with

the

cert

ifie

d va

lues

for A

l in

NIE

S M

usse

l, N

IST

Citr

us L

eave

s an

d O

yste

r T

issu

e. S

pike

reco

veri

es o

f 92

–104

% w

ere

also

obt

aine

d

135

Analyst, July 1998, Vol. 123 115R

Tab

le 2

Mic

row

ave

dige

stio

n pr

oced

ures

for

geo

logi

cal

sam

ples

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Sedi

men

tsa

mpl

esH

gPr

olab

o M

icro

dige

st 3

01O

n-lin

e di

gest

ion

of 0

.15%

slur

ries

(in

50%

HC

l),

incl

udin

g B

r2–B

rO32

oxid

atio

n of

org

anom

ercu

rysp

ecie

s

On-

line

anal

ysis

by

CV

-AA

SA

rec

over

y of

97%

was

obt

aine

d fo

r a

met

hylm

ercu

ry s

tand

ard.

Goo

d re

sults

wer

e ob

tain

ed f

or H

g in

NR

CC

PA

CS-

1 H

arbo

urM

arin

e Se

dim

ent

22

Sedi

men

tsa

mpl

esH

gPr

olab

o M

icro

dige

st 3

01O

pen

focu

sed

HN

O3–H

2SO

4–

H2O

2di

gest

ion

for

10 m

in(n

=1)

CV

-AA

SR

esul

ts w

ere

in a

gree

men

t w

ith t

he c

ertif

ied

valu

e fo

r N

RC

CPA

CS-

1 H

arbo

ur M

arin

e Se

dim

ent

22

Soil

and

sedi

men

tsa

mpl

es

Hg

Prol

abo

Mic

rodi

gest

301

On-

line

dige

stio

n of

slu

rrie

spr

epar

ed i

n ni

tric

aci

dO

n-lin

e FI

–CV

-AFS

anal

ysis

Goo

d re

sults

w

ere

obta

ined

fo

r St

ate

Bur

eau

of

Met

rolo

gy(C

hina

) Po

llute

d Fa

rm S

oil

and

Can

adia

n C

entr

e fo

r M

iner

alan

d E

nerg

y T

echn

olog

y L

ake

Sedi

men

t

24

Soil

and

sedi

men

tsa

mpl

es

As,

Cd,

Co,

Cr,

Cu,

Hg,

Mo,

Ni,

Pb, Z

n

Prol

abo

Mic

rodi

gest

A30

0an

d C

EM

MD

S-81

D(a

) C

lose

d ve

ssel

HC

l–H

NO

3–H

Fdi

gest

ion.

Ope

n fo

cuse

ddi

gest

ion

with

: (b

) H

NO

3–

H2O

2;

(c)

HC

l–H

NO

3–H

2O

2

ICP-

AE

S an

d IC

P-M

SG

ood

resu

lts

wer

e ob

tain

ed

for

BC

R

Am

ende

d So

il us

ing

proc

edur

e (b

) an

d fo

r E

stua

rine

Sed

imen

t (ex

cept

hig

h H

g an

dPb

) us

ing

proc

edur

es (

a) a

nd (

c)

25

Soil

sam

ples

Hg

Prol

abo

Max

idig

est

MX

350

and

CE

MM

DS-

81D

Ope

n an

d cl

osed

dig

estio

n w

ith(a

) 1

mH

Cl,

(b)

50%

HN

O3,

(c)

HN

O3, (

d) A

qua

regi

a

CV

-AA

S an

d E

TA

AS

For

the

open

dig

estio

n, r

esul

ts w

ere

low

for

NIS

T M

onta

na S

oil

whe

reas

goo

d re

sults

wer

e ob

tain

ed f

or t

he c

lose

d di

gest

ion

[pro

cedu

res

(a),

(b)

and

(d)

]

136

Sedi

men

tsa

mpl

esA

sPr

olab

o A

300

and

CE

MM

DS-

81D

Ope

n fo

cuse

d di

gest

ion

with

(a)

HC

l–H

NO

3–H

2O

2fo

r 35

min

(tot

al A

s), (

b) H

NO

3–H

Cl

for

12 m

in (

As

spec

iatio

n). C

lose

ddi

gest

ion

with

: (c

) H

NO

3–

HC

lO4–H

F–H

Cl

for

1h (

tota

lA

s)

ICP-

MS

and

ICP-

AE

S(f

or t

otal

ars

enic

)H

PLC

–IC

P-M

S (f

or A

ssp

ecia

tion)

In t

he l

ake

sedi

men

t an

alys

ed, t

he A

s sp

ecie

s D

MA

, MM

A a

ndA

sVw

ere

stab

le d

urin

g th

e m

icro

wav

e ex

trac

tion

proc

edur

e.A

sIII

was

oxi

dise

d to

AsV

, bu

t th

is w

as r

educ

ed b

y ex

trac

tion

with

ort

hoph

osph

ate

or a

mm

oniu

m o

xala

te.

An

extr

actio

nyi

eld

for

tota

l A

s of

100

% w

as o

btai

ned

for

the

mic

row

ave

extr

actio

n pr

oced

ure

(cal

cula

ted

as %

of

the

yiel

d ob

tain

ed b

yth

e to

tal

As

proc

edur

es)

137

Sedi

men

tsa

mpl

esH

gPr

olab

o M

axid

iges

t(3

00W

)O

n-lin

e di

gest

ion

of s

lurr

ies

prep

ared

in

aqua

reg

ia–

KM

nO4

On-

line

anal

ysis

by

FIm

ercu

ry s

yste

mG

ood

resu

lts w

ere

obta

ined

for N

IST

Buf

falo

Sed

imen

t, al

thou

ghth

ose

for

NR

CC

BC

SS-1

Mar

ine

Sedi

men

t wer

e sl

ight

ly h

igh.

Goo

d sp

ike

reco

veri

es w

ere

also

obt

aine

d

138

Soil

sam

ples

Cu,

Fe,

Zn

Prol

abo

Mic

rodi

gest

301

Aut

omat

ed D

TPA

–CaC

l 2–

trie

than

olam

ine

extr

actio

nus

ing

a ro

botic

sta

tion

(5sa

mpl

es h2

1)

Aut

omat

ed c

entr

ifug

atio

nan

d tr

ansp

ort

to F

AA

ST

he e

xtra

ctio

n ef

fici

ency

of Z

n is

com

para

ble

to th

e co

nven

tiona

lte

chni

que,

whe

reas

a g

reat

er e

ffic

ienc

y re

sulte

d fo

r Fe

and

Cu

139

Sedi

men

tsa

mpl

esH

gPr

olab

o M

icro

dige

st A

301

Ope

n fo

cuse

d H

NO

3di

gest

ion

for

5 m

in, f

ollo

wed

by

5 m

inco

olin

g an

d he

atin

g w

ith H

2O

2

(5 m

in)

FI–I

CP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or H

g in

NR

CC

PA

CS-

1 H

arbo

urM

arin

e Se

dim

ent,

IAE

A-3

56 a

nd B

CR

S19

sed

imen

t sam

ples

.Sa

mpl

es f

rom

Arc

ahon

Bay

wer

e al

so a

naly

sed

140

Dus

t an

d ai

rfi

lters

PbC

EM

Spe

ctro

Prep

O

n-lin

e m

icro

wav

e di

gest

ion

ofsl

urri

ed s

ampl

es (

prep

ared

in

3m

HN

O3);

10

min

per

sam

ple

Off

-lin

e an

alys

is b

y ID

–IC

P-M

SG

ood

resu

lts f

or P

b w

ere

obta

ined

in

NIS

T S

RM

267

6d T

oxic

Met

als

on F

ilter

s32

Coa

l sa

mpl

esC

a, C

d, F

e,M

g, Z

n C

EM

MD

S-81

O

n-lin

e st

oppe

d-fl

ow d

iges

tion

ofsl

urri

es (

in T

rito

n X

-100

and

HN

O3)

for

5 m

in p

er s

ampl

e

Off

-lin

e an

alys

is b

y A

AS

Inco

mpl

ete

dige

stio

n of

coa

l re

sulte

d35

Soil

sam

ples

As,

Se

CE

M M

DS-

2000

H2O

–HN

O3–H

Cl–

HF

PTFE

bom

b di

gest

ion

for

30 m

inH

G–A

AS

Goo

d re

sults

for

MR

G-1

sili

cate

d ro

cks

(Can

ada

Cen

tre

for

Min

eral

and

Ene

rgy

Tec

hnol

ogy)

and

spi

ke r

ecov

erie

s of

95%

wer

e ob

tain

ed

38

116R Analyst, July 1998, Vol. 123

Tab

le 2

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Geo

logi

cal

sam

ples

As,

Ba,

Cd,

Co,

Cr,

Cu,

Hg,

Mn,

Ni,

Pb, S

b, T

l,V

, Zn

CE

M M

DS-

81D

HN

O3

Tef

lon

bom

b di

gest

ion

(18

min

) fo

llow

ed b

y 21

min

heat

ing

with

HF.

H2O

2is

the

nad

ded

and

heat

ing

cont

inue

d in

a w

ater

-bat

h (1

5 m

in)

befo

read

ding

H3B

O3

for

a fu

rthe

r5–

10 m

in (

n=

12)

AA

S an

d IC

P-A

ES

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

SR

M 2

704

Buf

falo

Riv

erSe

dim

ent,

exce

pt f

or h

igh

Sb a

nd T

l, sl

ight

ly l

ow C

o an

d C

uan

d sl

ight

ly h

igh

As,

Cr a

nd M

n. T

he m

etho

d w

as d

evel

oped

toan

alys

e fe

rtili

zers

an

d so

il am

endm

ents

in

clud

ing

rock

phos

phat

es, l

imin

g m

ater

ials

org

anic

mat

eria

l and

san

dy lo

amso

il

45

Soil

sam

ples

As,

Se

CE

M M

DS-

81D

PFA

bom

b di

gest

ion

for

1–2

hw

ith:

(a)

HN

O3–H

Cl,

(b)

H2O

2–H

Cl–

H2SO

4, (

c) H

2O

2–

H2SO

4, (

d) H

NO

3–H

2SO

4

FI–H

G–A

AS

Met

hod

(d)

gave

the

bes

t re

cove

ries

(va

lidat

ed u

sing

NIS

T S

anJo

aqui

n So

il).

Goo

d re

sults

wer

e ob

tain

ed f

or A

s, b

ut S

ere

cove

ries

wer

e sl

ight

ly h

igh.

Met

hod

used

to a

naly

se s

ewag

esl

udge

(se

e T

able

1)

51

Sedi

men

tsa

mpl

esA

s, C

d, C

o, C

r,C

u, M

n, N

i,Pb

, Zn

CE

M S

pect

roPr

ep s

yste

mO

n-lin

e di

gest

ion

of 1

% s

lurr

ies

(in

20%

HF,

50%

HN

O3

and

10%

HC

l)

ICP-

MS,

IC

P-A

ES

(for

Fe

and

Al)

and

ET

AA

S(f

or A

s)

Goo

d re

sults

wer

e ob

tain

ed f

or A

s, C

d, C

o, C

u, F

e, M

n, N

i, Pb

and

Zn

in N

RC

C B

CSS

-1 M

arin

e Se

dim

ent,

how

ever

, res

ults

for

Cr

and

Al

wer

e lo

w

54

Sedi

men

tsa

mpl

esH

gC

EM

MD

S-20

00H

NO

3PT

FE b

omb

dige

stio

n fo

r70

sC

V-A

AS

Res

ults

wer

e in

goo

d ag

reem

ent

with

the

pro

visi

onal

val

ue f

orN

IES

No.

2 P

ond

Sedi

men

t12

1

Phos

phat

icfe

rtili

sers

and

anim

alfe

edst

uffs

As,

B, B

a, B

i,C

d, C

o, C

r,C

u, H

g, M

n,M

o, N

i, Pb

,Se

, Sb,

V,

W, Z

n

CE

M M

DS-

81D

PTFE

bom

b di

gest

ion

with

(a)

HN

O3, (

b) H

Cl–

HN

O3–

HC

lO4–H

F

ICP-

MS

For N

IST

Buf

falo

Riv

er S

edim

ent:

(a) R

esul

ts fo

r As,

Cd,

Co,

Cu,

Ni a

nd P

b w

ere

good

, but

thos

e fo

r Ba,

Cr,

Mn,

Sb,

V, Z

n w

ere

low

and

Hg

was

hig

h; (

b) R

esul

ts f

or A

s, C

o, C

u an

d N

i wer

ego

od; B

a, H

g an

d V

res

ults

wer

e be

tter

than

for

(a)

, but

Ni,

Zn

and

Sb w

ere

high

and

Cr

low

. R

esul

ts f

or N

BS

Flor

ida

Phos

phat

e R

ock

by p

roce

dure

(a)

gen

eral

ly a

gree

d w

ell

with

the

cert

ifie

d an

d in

form

atio

nal

valu

es

141

Sedi

men

tsa

mpl

esC

o, C

u, M

n,Pb

, Zn

CE

M M

DS-

81D

18 d

iges

tion

proc

edur

es w

ithdi

ffer

ent

com

bina

tions

of

HN

O3, H

2O

2, H

F an

d H

Cl

FAA

S an

d L

’vov

pla

tfor

m(f

or C

o)PC

A a

nd m

ultic

rite

ria

deci

sion

mak

ing

met

hods

PR

OM

ET

HE

Ean

d G

AIA

sel

ecte

d an

HC

l–H

NO

3–H

Cl

dige

stio

n as

the

bes

tfo

r N

BS

Buf

falo

Riv

er S

edim

ent

142

Sedi

men

t an

dro

ck s

ampl

esC

o, C

r, C

u, N

i,Pb

, Zn

CE

M M

DS-

81D

14 d

iges

tion

proc

edur

es w

ithdi

ffer

ent

com

bina

tions

of

HF,

HN

O3, H

Cl,

H2O

2an

d ac

etic

acid

FAA

SPC

A,

SIM

CA

, PR

OM

OT

HE

E,

GA

IA a

nd F

uzzy

Clu

ster

ing

chem

omet

ric

tech

niqu

es s

elec

ted

an H

NO

3–H

F di

gest

ion

asth

e be

st p

roce

dure

for

NB

S B

uffa

lo R

iver

Sed

imen

t an

d ‘I

nH

ouse

’ se

cond

ary

rock

sta

ndar

d

143

Sedi

men

tsa

mpl

esC

dC

EM

MD

S-81

DH

NO

3T

eflo

n bo

mb

dige

stio

n fo

r80

min

(n

=12

)E

TA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

Sed

imen

ts 1

646

and

2704

.R

esul

ts w

ere

in g

ood

agre

emen

t w

ith t

hose

obt

aine

d fr

om a

conv

entio

nal

HF–

HC

lO4

dige

stio

n un

dert

aken

in

plat

inum

cruc

ible

s

144

Sedi

men

tsa

mpl

esC

r(a

) C

EM

MD

S-81

,(b

) Fl

oyd

RM

S-15

0,(c

) M

ilest

one

ML

S 12

00M

EG

A

HC

l–H

NO

3–H

F–H

ClO

4PT

FEbo

mb

dige

stio

n: (

a) h

eate

d to

1200

psi

g, c

oole

d an

d re

peat

ed3

2, (

b) h

eate

d fo

r 20

min

at

med

ium

pre

ssur

e, (

c) h

eate

dfo

r 26

.5 m

in a

t hi

gh p

ress

ure.

Aft

er c

oolin

g al

l sa

mpl

es w

ere

evap

orat

ed t

o dr

ynes

s on

a h

ot-

plat

e an

d so

lubi

lised

in

HN

O3

FAA

S an

d IC

P-A

ES

Usi

ng p

roce

dure

(b)

, res

ults

wer

e ob

tain

ed in

agr

eem

ent w

ith th

ece

rtif

ied

valu

e fo

r NIS

T S

RM

270

4 B

uffa

lo R

iver

Sed

imen

t. A

mea

n sp

ike

reco

very

(for

all

proc

edur

es) o

f 98%

was

obt

aine

d.H

owev

er, l

ow r

esul

ts w

ere

obta

ined

for

Cr

in N

RC

C B

CSS

-1M

arin

e Se

dim

ent f

ollo

win

g pr

oced

ures

(a),

(b) a

nd (c

) and

als

oby

an

open

hot

-pla

te m

etho

d. I

t w

as c

oncl

uded

tha

t no

aci

ddi

ssol

utio

n pr

oced

ures

are

ade

quat

e fo

r the

det

erm

inat

ion

of C

rin

thi

s sa

mpl

e

145

Sedi

men

tsa

mpl

esC

r, C

u, H

g,M

n, N

i, Pb

,Z

n

CE

M M

DS-

81D

PTFE

bom

b di

gest

ion

(n=

12)

with

(a)

aqu

a re

gia

(80

min

),(b

) aq

ua r

egia

–HF

(80

min

)

AA

S an

d C

V-A

AS

(for

Hg)

For p

roce

dure

(a),

resu

lts w

ere

gene

rally

low

for N

RC

C M

ESS

-1E

stua

rine

Sed

imen

t an

d PA

CS-

1 H

arbo

ur M

arin

e Se

dim

ent.

Res

ults

wer

e sl

ight

ly i

mpr

oved

aft

er d

iges

tion

by p

roce

dure

(b),

but

mos

t res

ults

wer

e st

ill n

ot in

goo

d ag

reem

ent w

ith th

ece

rtif

ied

valu

es

146

Analyst, July 1998, Vol. 123 117R

Tab

le 2

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Dus

t, as

hes

and

sedi

men

tsA

l, A

s, B

a, B

e,C

a, C

o, C

r,C

u, F

e, M

g,M

n, N

i, Pb

,S,

Sb,

Ti,

V,

Zn

CE

M M

DS-

81D

Tef

lon

PFA

bom

b di

gest

ion

for

22 m

in (

n=

6) w

ith (

a)H

NO

3–H

Cl

(aci

d so

lubl

eel

emen

ts),

(b)

HN

O3–H

Cl–

HF

with

H3B

O3

neut

ralis

atio

n(t

otal

dig

estio

n)

ICP-

AE

S(a

) R

ecov

erie

s ob

tain

ed f

or d

iffe

rent

ele

men

ts i

n th

e ra

nge:

NR

CC

M

ESS

-1

Est

uari

ne

Sedi

men

t 25

–103

%,

NR

CC

PAC

S-1

Har

bour

Mar

ine

Sedi

men

t 38

–99%

, N

IST

Coa

l Fl

yA

sh:

60–1

03%

, ‘i

n-ho

use’

dus

t: 23

–100

%.

(b)

Goo

d re

sults

wer

e ob

tain

ed f

or C

oal

Fly

Ash

(ex

cept

low

Co)

and

for

ME

SS-1

(ex

cept

low

Ti)

. Fo

r PA

CS-

1 re

sults

wer

e go

od,

exce

pt f

or A

l, Fe

, C

a, M

g, N

i an

d S

(jus

t ou

tsid

e ce

rtif

ied

rang

e)

147

Sedi

men

tsa

mpl

esA

s, H

g, S

eC

EM

MD

S-81

DPF

A b

omb

dige

stio

n w

ith (

a)H

2SO

4–H

NO

3–H

Cl

(As

and

Se),

(b)

HN

O3

(Hg)

FI–A

AS

(As

and

Se)

and

CV

-AA

S (H

g)G

ood

resu

lts w

ere

obta

ined

for

pro

pose

d N

IST

SR

M 1

646a

Est

uari

ne S

edim

ent

and

SRM

270

4 B

uffa

lo R

iver

Sed

imen

t.R

esul

ts w

ere

in g

ood

agre

emen

t w

ith t

hose

of

a tr

aditi

onal

refl

ux d

iges

tion

148

Mol

ybde

nite

min

eral

Os

CE

M M

DS-

81D

HN

O3–H

2SO

4PT

FE b

omb

dige

stio

n fo

r 45

min

fol

low

edby

hea

ting

with

K2C

r 2O

7.

Os

dist

illat

ion

prio

r to

ICP-

MS

anal

ysis

The

tec

hniq

ue w

as a

pplie

d to

Re–

Os

age

dete

rmin

atio

n in

ana

tura

l m

olyb

deni

te s

ampl

e. R

esul

ts w

ere

in a

gree

men

t w

ithth

ose

obta

ined

by

a

U–P

b m

etho

d fo

r zi

rcon

(a

ssoc

iate

dm

iner

al)

149

Mar

ine

sedi

men

tsa

mpl

es

Al,

Ca,

Cr,

Cu,

Fe, M

n, N

i,Pb

, Zn

CE

M M

DS-

2000

and

Mile

ston

e L

AV

IS-1

000

mul

tiMO

IST

mic

row

ave

dryi

ngsy

stem

HN

O3

bom

b di

gest

ion

follo

win

gm

icro

wav

e dr

ying

of

the

sam

ple

by t

he t

wo

met

hods

(15

min

)

ICP-

AE

S an

d FA

AS

(for

Pb)

No

sign

ific

ant

diff

eren

ces

wer

e fo

und

betw

een

the

moi

stur

eco

nten

t of

mar

ine

sedi

men

t dr

ied

by t

radi

tiona

l ov

en a

ndva

cuum

mic

row

ave

dryi

ng t

echn

ique

s. S

imila

r re

sults

wer

eob

tain

ed f

or th

e tr

ace

met

al a

nd to

tal c

arbo

n co

nten

t of

mar

ine

sedi

men

ts d

ried

by

the

two

met

hods

150

Geo

logi

cal

sam

ples

Ba,

Be,

Co,

Cr,

Cs,

Cu,

Hf,

Mo,

Ni,

Nb,

Pb, R

b, S

b,Sc

, Sn,

Sr,

Ta,

Th,

Tl,

U, W

, Zn,

Zr

and

RE

Es

CE

M M

DS-

81D

PFA

bom

b H

NO

3–H

F–H

ClO

4

dige

stio

n fo

r 63

min

(n

=4)

,fo

llow

ed b

y ho

t-pl

ate

evap

orat

ion

to d

ryne

ss w

ithH

ClO

4an

d di

ssol

utio

n in

HN

O3

ICP-

AE

S an

d IC

P-M

SG

ener

ally

acc

epta

ble

resu

lts w

ere

obta

ined

for

Ba,

Be,

Co,

Cs,

Cu,

Ni,

Nb,

Pb,

Rb,

Sb,

Sn,

Sr,

Ta,

Th,

Tl,

U, W

, Zn

and

for

mos

t of

the

RE

Es

in a

ran

ge o

f ge

olog

ical

CR

Ms

(sed

imen

tsan

d ro

cks)

. The

acc

urac

y of

Cr,

Hf,

Mo,

Sc,

Zr

dete

rmin

atio

nsva

ried

with

the

sam

ple

type

, whe

reas

Y re

cove

ries

wer

e lo

w in

the

nine

CR

Ms

anal

ysed

151

Geo

logi

cal

sam

ples

Au,

Ir,

Pd,

Rh,

R

u, P

tC

EM

MD

S-81

D

(a)

Low

pre

ssur

e H

NO

3–H

Cl–

HF–

HC

lO4

dige

stio

n.(b

) H

igh

pres

sure

aqu

a re

gia–

HF

dige

stio

n. R

esid

ues

wer

efu

sed

with

Na 2

CO

3–N

a 2O

2–

ICP-

MS

Proc

edur

e (a

) w

as e

mpl

oyed

for

the

dig

estio

n of

sul

fide

-ric

hsa

mpl

es a

nd p

roce

dure

(b)

for

sili

cate

, su

lfid

e an

d ch

rom

itite

sam

ples

. CR

Ms

wer

e al

so a

naly

sed

152

Air

born

epa

rtic

ulat

eson

Tef

lon

filte

rs

Al,

As,

Ba,

Cd,

Cr,

Cu,

Fe,

K, M

g, M

n,N

a, N

i, Pb

,Sb

, V, Z

n

CE

M M

DS-

2000

HC

l–H

NO

3–H

ClO

4–H

F di

gest

ion

(32

min

) fo

llow

ed b

y op

enve

ssel

eva

pora

tion

of H

F (2

5m

in)

(n=

12)

ICP-

MS

Gen

eral

ly l

ow r

esul

ts w

ere

obta

ined

for

NIS

T U

rban

Par

ticul

ate

Mat

ter

[acc

redi

ted

in p

art t

o th

e lo

w m

ass

of s

ampl

e us

ed (

0.1

mg)

]. H

ighe

r re

cove

ries

wer

e ob

tain

ed w

ith a

con

vent

iona

lpr

essu

re b

omb

dige

stio

n al

thou

gh t

he d

iges

tion

time

was

10

times

hig

her

153,

154

Air

born

epa

rtic

ulat

eson

gla

ss-

fibr

e fi

lters

Al,

Fe, K

, Mg,

S, Z

nC

EM

MD

S-20

00H

NO

3–H

ClO

4PT

FE b

omb

dige

stio

n fo

r 9

min

fol

low

edby

coo

ling,

rem

oval

of

filte

rre

sidu

e, h

eatin

g w

ith H

F (9

min

) an

d H

3B

O3

neut

ralis

atio

nof

HF

ICP-

AE

SR

ecov

erie

s of

90–

101%

wer

e ob

tain

ed f

or A

l, Fe

, K, M

g, S

and

Zn

in N

IST

Urb

an P

artic

ulat

e M

atte

r15

5

Air

born

epa

rtic

ulat

em

atte

r on

filte

rs

As

CE

M M

DS-

2000

HN

O3–H

ClO

4PT

FE b

omb

dige

stio

n, f

ollo

wed

by

cool

ing,

rem

oval

of

filte

r an

d fu

rthe

rhe

atin

g w

ith H

ClO

4–H

F (t

otal

18 m

in).

HF

rem

oved

by

evap

orat

ion

ICP-

MS

A r

ecov

ery

for

As

of 1

07.4

% w

as o

btai

ned

in N

IST

(SR

M 1

648)

Urb

an P

artic

ulat

e M

atte

r15

6

118R Analyst, July 1998, Vol. 123

Tab

le 2

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Roc

k sa

mpl

es59

maj

or a

ndtr

ace

elem

ents

CE

M M

DS-

2000

HN

O3–H

F–H

ClO

4T

eflo

n bo

mb

dige

stio

n fo

r 0.

5–1

h (n

=9)

.A

fter

coo

ling

sam

ples

are

tran

sfer

red

to b

eake

rs f

or h

ot-

plat

e ev

apor

atio

n to

dry

ness

.H

NO

3is

the

n ad

ded,

and

sam

ples

tak

en t

o dr

ynes

s ag

ain

ICP-

MS

Res

ults

wer

e pr

esen

ted

for

59 e

lem

ents

in G

eolo

gica

l Soc

iety

of

Japa

n ro

ck r

efer

ence

mat

eria

ls J

B-1

Bas

alt,

JB-3

Bas

alt,

JG-1

Gra

nodi

orite

, JR

-2

Rhy

olite

, JG

b-1

Gab

bro

and

JA-2

And

esite

157

Sedi

men

tsa

mpl

esC

d, C

r, C

o,C

u, F

e, M

n,N

i, Pb

, Se,

Zn

CE

M M

DS-

2000

HF–

HC

l–H

NO

3PT

FE b

omb

dige

stio

n fo

r 15

min

(n

=12

)FA

AS

and

ET

AA

S O

rtho

gona

l ar

ray

desi

gn w

as a

pplie

d to

the

opt

imis

atio

n of

dige

stio

n pa

ram

eter

s. G

ener

ally

goo

d re

sults

wer

e ob

tain

ed fo

rN

BS

Buf

falo

R

iver

Se

dim

ent,

NR

CC

B

CSS

-1

Mar

ine

Sedi

men

t an

d N

IES

Pond

Sed

imen

t

158

Sedi

men

tsa

mpl

esH

gC

EM

MD

S-20

00PT

FE b

omb

clos

ed d

iges

tion

for

30 m

in (

n=

12)

with

(a)

HN

O3–H

2SO

4, (

b) H

NO

3–

HC

lO4

(c)

HN

O3–H

Cl,

(d)

HN

O3–H

Cl–

HF

FI–C

V-A

AS

Goo

d re

sults

wer

e ob

tain

ed fo

r NIS

T S

RM

164

5 R

iver

Sed

imen

t,N

RC

C B

CSS

-1 M

arin

e Se

dim

ent,

NIE

S C

RM

No.

2 P

ond

Sedi

men

t an

d in

a m

ixtu

re o

f th

e la

tter

and

NIS

T S

RM

151

5A

pple

Lea

ves

(cho

sen

to g

ive

the

sam

ple

an o

rgan

ic m

atte

rco

nten

t of

10

%).

Pr

oced

ures

(c

) an

d (d

) w

ere

the

mos

tef

fect

ive.

Spi

ke r

ecov

erie

s of

94-

104%

wer

e ob

tain

ed f

orse

dim

ent

and

soil

sam

ples

159

Soil

and

sedi

men

tsa

mpl

es

Cu,

Cr,

Mn,

Pb, Z

nC

EM

MD

S-20

00H

Cl–

HN

O3–H

F PT

FE b

omb

dige

stio

n fo

r 30

min

(n

=12

)FA

AS

and

ET

AA

SM

ixed

-lev

el

orth

ogon

al

arra

y de

sign

w

as

appl

ied

to

the

optim

isat

ion

of

dige

stio

n pa

ram

eter

s.

For

the

optim

ised

proc

edur

e, g

ener

ally

goo

d re

sults

wer

e ob

tain

ed fo

r NB

S SR

M16

45 R

iver

Sed

imen

t, N

IES

No.

2 P

ond

Sedi

men

t (ex

cept

low

Cr)

and

NR

CC

BC

SS-1

Mar

ine

Sedi

men

t

160

Sedi

men

tsa

mpl

esA

s, S

eC

EM

MD

S-20

00C

lose

d di

gest

ion

for

30 m

in(n

=12

) w

ith (

a) H

NO

3–

H2SO

4, (

b) H

NO

3–H

ClO

4, (

c)H

NO

3–H

Cl,

(d)

HN

O3–H

Cl–

HF,

(e)

HN

O3–H

2SO

4–H

ClO

4

FI–H

G–A

AS

Goo

d re

sults

wer

e ob

tain

ed b

y al

l pr

oced

ures

for

NIS

T S

RM

1645

Riv

er S

edim

ent,

how

ever

pro

cedu

res

(a),

(b) a

nd (e

) wer

eno

t re

com

men

ded

owin

g to

the

pot

entia

l ha

zard

ous

natu

re o

fth

e di

gest

ion

envi

ronm

ent.

No

effe

ct t

o th

e di

gest

ion

was

obse

rved

fol

low

ing

the

addi

tion

of S

RM

151

5 A

pple

Lea

ves

(to

give

an

or

gani

c co

nten

t of

10

%).

G

ood

resu

lts

wer

eob

tain

ed b

y pr

oced

ures

(c)

and

(d)

for

NR

CC

BC

SS-1

and

NIE

S C

RM

N

o.

2 Po

nd

Sedi

men

t. Sp

ike

reco

veri

es

of94

–104

% w

ere

obta

ined

for

sed

imen

t sa

mpl

es

161

Cor

al s

oil

sam

ples

SiFl

oyd

RM

S-15

0H

NO

3–H

2O

2–H

F T

eflo

n bo

mb

dige

stio

n fo

r 25

min

ICP-

AE

S fo

llow

ing

addi

tion

of H

3B

O3

and

a te

rtia

ry a

min

e m

ixtu

re

Acc

epta

ble

agre

emen

t w

ith t

he r

esul

ts o

btai

ned

from

an

LiB

O2

fusi

on p

roce

dure

was

obt

aine

d fo

llow

ing

mic

row

ave

dige

stio

nof

five

cor

al s

oil s

ampl

es. T

he a

vera

ge p

reci

sion

of t

he m

etho

dw

as 7

%

19

Soil

and

dust

As

Floy

d R

MS-

150

HN

O3–H

2O

2bo

mb

dige

stio

n fo

r32

min

(n

=6)

ICP-

MS

Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

Urb

an P

artic

ulat

e M

atte

ran

d IA

EA

Soi

l 7

77

Sedi

men

tsa

mpl

esC

d, C

r, C

u, P

b,N

i, Sb

, Sn,

Th

Floy

dSa

mpl

es w

ere

dige

sted

with

HN

O3–H

F fo

r 52

min

,ev

apor

ated

to

dryn

ess

on a

hot

-pl

ate

and

diss

olve

d in

HN

O3–

H2O

ID–I

CP-

MS,

IC

P-M

S an

dE

TA

AS

Goo

d re

sults

wer

e ob

tain

ed f

or C

d, C

r, C

u, P

b, N

i, Sb

, Sn

and

Th

in a

Mis

siss

ippi

Riv

er d

elta

sed

imen

t sa

mpl

e (N

OA

A/7

)78

Dus

t sa

mpl

esC

d, P

bFl

oyd

RM

S-15

0T

eflo

n bo

mb

dige

stio

n fo

r 20

min

with

(a)

HN

O3, (

b) H

Cl–

HN

O3, (

c) H

NO

3–H

F

DP-

ASV

and

FA

AS

Dig

estio

n ef

fici

enci

es o

f 85

–95%

wer

e ob

tain

ed (

RSD

= 1

0%)

for

NB

S U

rban

Pa

rtic

ulat

e M

atte

r,

BC

R

City

W

aste

Inci

nera

tion

Ash

an

d R

iver

Se

dim

ent.

No

sign

ific

ant

diff

eren

ces

wer

e fo

und

betw

een

the

resu

lts

of

the

thre

em

icro

wav

e m

etho

ds

and

a st

anda

rd

hot-

plat

e di

gest

ion

met

hod

162

Analyst, July 1998, Vol. 123 119R

Tab

le 2

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Geo

logi

cal

sam

ples

Al,

Fe, K

, Mg,

Na,

Si

Mile

ston

e M

LS-

1200

PT

FE b

omb

dige

stio

n.C

oal:

HN

O3–H

2O

2–H

F–H

ClO

4.

Lim

esto

ne:

HC

l–H

F.Ir

on O

res:

HC

l

ICP-

AE

S an

d A

AS

Res

ults

for l

imes

tone

sam

ples

wer

e in

goo

d ag

reem

ent w

ith th

ose

obta

ined

by

XR

F. F

e le

vels

in

BC

S N

IMB

A F

e O

re,

Fe O

reSi

nter

and

Lin

coln

shir

e Fe

Ore

wer

e w

ithin

the

cer

tifie

dra

nge

72

Sedi

men

tsa

mpl

esA

s, A

l, C

d, C

r,C

o, C

u, F

e,M

n, N

i, Pb

,Sn

, Ti,

Zn

Mile

ston

e M

LS-

1200

ME

GA

Tef

lon

bom

b di

gest

ion

for

25 m

in(n

=6)

with

(a)

HN

O3–H

F–H

3PO

4–H

3B

O3, (

b) H

NO

3–

HC

l–H

F–H

3B

O3, (

c)E

xtra

ctio

n w

ith H

NO

3

ICP-

AE

S [f

or (

a) a

nd (

b)]

and

TX

RF

[for

(c)

]R

esul

ts f

or B

CR

320

Riv

er S

edim

ent w

ere

follo

ws:

(a)

goo

d fo

rA

l, Fe

, Mn,

low

for

Cr,

Cu

and

Zn

and

high

for

Co;

(b)

goo

dfo

r Al,

Fe, C

u; h

igh

for

Co

and

slig

htly

low

for

Cr,

Mn,

Zn;

(c)

good

for A

s, h

igh

for N

i, sl

ight

ly lo

w fo

r Cu,

Fe,

Pb

and

Zn

and

very

low

for

Cr

and

Sn

163

Sedi

men

tsa

mpl

es50

ele

men

tsM

ilest

one

ML

S-12

00H

NO

3–H

F T

eflo

n bo

mb

dige

stio

nfo

r 19

min

, fol

low

ed b

yev

apor

atio

n to

dry

ness

(90

min

) an

d di

ssol

utio

n in

HC

l

ICP-

MS

and

TX

RF

Goo

d re

sults

wer

e ob

tain

ed fo

r Al,

Ca,

Fe,

K, M

g, N

a, P

b, R

b, S

r,T

i and

V in

NR

CC

ME

SS-1

Est

uari

ne S

edim

ent;

how

ever

, Ba

resu

lts w

ere

high

and

Zn

low

164

Roc

k an

dse

dim

ent

sam

ples

Th,

U, Y

and

lant

hani

des

Mile

ston

e M

LS-

1200

ME

GA

HF–

HN

O3–H

Cl

Tef

lon

bom

bdi

gest

ion

for

16 m

in, f

ollo

wed

by h

eatin

g w

ith H

3B

O3

and

ED

TA

for

8 m

in

ICP-

MS

Res

ults

wer

e pr

esen

ted

for

USG

S A

ndes

ite (

AG

V-1

), B

asal

t(B

CR

-1,

BH

VO

-1),

Dia

base

(W

-2,

DN

C-1

), G

rani

te (

G-2

),M

arin

e M

ud (

MA

G-1

), f

or C

CR

MP

Syen

ite (

SY-2

), G

abbr

o(M

RG

-1),

Lak

e Se

dim

ents

(L

KSD

-1,4

), S

trea

m S

edim

ents

(ST

SD-1

,4)

and

for

NIM

-G G

rani

te, B

E-N

Bas

alt,

GSD

-1,5

,6St

ream

Sed

imen

t an

d N

BS

SRM

164

5 R

iver

Sed

imen

t

165

Air

born

epa

rtic

ulat

eson

PT

FEfi

lters

Al,

As,

Cd,

Cr,

Cu,

Fe,

K,

Mg,

Ni,

Pb,

S, S

b, V

, Zn

Mile

ston

e M

LS-

1200

HN

O3–H

ClO

4–H

F PT

FE b

omb

dige

stio

n fo

r 8

min

FAA

S, E

TA

AS,

IC

P-A

ES

and

ICP-

MS

Goo

d re

sults

wer

e ob

tain

ed fo

r As,

Cd,

Cu,

Fe,

Mg,

Ni,

S, S

b an

dZ

n in

NIS

T U

rban

Par

ticul

ate

Mat

ter;

how

ever

K,

Pb a

nd V

resu

lts w

ere

slig

htly

low

and

Al

and

Cr

very

low

166

Coa

l sa

mpl

esR

EE

sM

ilest

one

ML

S-12

00PT

FE b

omb

dige

stio

n w

ithH

NO

3–H

2O

2–H

F–H

Cl

HPI

C w

ith U

V/V

ISde

tect

ion

and

on-l

ine

prec

once

ntra

tion

Acc

epta

ble

agre

emen

t was

obt

aine

d w

ith th

e pu

blis

hed

valu

es fo

rN

BS

1632

a, S

AR

M-1

8, 1

9 an

d 20

coa

l C

RM

s (n

ot c

ertif

ied)

167

Bag

hous

e du

stH

gQ

uest

ron

Q-W

ave

1000

HN

O3

Tef

lon

bom

b di

gest

ion

CV

-AA

SN

o st

atis

tical

dif

fere

nce

was

obs

erve

d be

twee

n th

e re

sults

for

atr

aditi

onal

wat

er b

ath

met

hod

and

the

mic

row

ave

dige

stio

nm

etho

d

168

Geo

logi

cal

sam

ples

Al,

Ag,

As,

Ba,

Bi,

Cd,

Co,

Cr,

Cu,

Fe,

Li,

Mg,

Mn,

Mo,

Ni,

Pb,

Sb, S

n, S

r,T

h, T

i, T

l,U

, V, Z

n

Que

stro

n Q

-Wav

e 10

00H

NO

3–H

F–H

2O

2T

eflo

n bo

mb

dige

stio

n fo

r 25

min

. Aft

erco

olin

g, H

3B

O3

is a

dded

and

heat

ing

cont

inue

d fo

r a

furt

her

15 m

in (

n=

12)

ICP-

MS

Res

ults

wer

e pr

esen

ted

for N

IST

SR

M 1

633b

Coa

l Fly

Ash

, SR

M16

48

Urb

an

Part

icul

ate

Mat

ter,

SR

M

1646

E

stua

rine

Sedi

men

t, SR

M 2

704

Buf

falo

Riv

er S

edim

ent,

SRM

270

9 Sa

nJo

aqui

n So

il B

asel

ine

Tra

ce E

lem

ent,

SRM

271

1 M

onta

na S

oil

Mod

erat

ely

Ele

vate

d T

race

Ele

men

t an

d SR

M 2

700

Mon

tana

Soil

Hig

hly

Ele

vate

d T

race

Ele

men

t

169

Mar

ine

sedi

men

tsPb

Port

land

DM

R-1

40H

NO

3–H

Cl

PTFE

bom

b di

gest

ion

for

10 m

inE

TA

AS

Res

ults

for N

RC

C P

AC

S-1

Har

bour

Mar

ine

Sedi

men

t wer

e go

odan

d sp

ike

reco

veri

es o

f 95

–99%

wer

e ob

tain

ed.

Res

ults

wer

eco

mpa

red

with

tho

se o

btai

ned

by a

slu

rry

met

hod

170

Coa

l fl

y as

hA

s, S

eC

omm

erci

al o

ven

(650

W)

HC

l–H

NO

3–H

2SO

4Pa

rr b

omb

dige

stio

n fo

r 2 3

3 m

in w

ithin

teri

m c

oolin

g st

ep (

15 m

in).

Sam

ple

then

hea

ted

in a

wat

er-

bath

for

30

min

to

rem

ove

nitr

ates

HG

–AA

S an

alys

isfo

llow

ing

pre-

redu

ctio

nw

ith K

I an

d as

corb

icac

id

Res

ults

for

As

and

Se in

NIS

T 1

633b

Coa

l Fly

Ash

wer

e in

goo

dag

reem

ent

with

th

e ce

rtif

ied

valu

es

and

with

th

e re

sults

obta

ined

by

an N

aOH

fus

ion

proc

edur

e

171

Sedi

men

ts,

geol

ogic

alsa

mpl

es

Hg

Dom

estic

ove

n (8

00 W

)H

NO

3PT

FE b

omb

dige

stio

n fo

r3

min

at

800

W (

n=

5)FA

NE

S af

ter

redu

ctio

nw

ith S

nCl 2

and

in s

itu

prec

once

ntra

tion

Res

ults

for

NIS

T R

iver

Sed

imen

t w

ere

slig

htly

low

85

120R Analyst, July 1998, Vol. 123

Tab

le 2

Con

tinu

ed

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Sedi

men

tssa

mpl

esC

rD

omes

tic o

ven

(650

W)

Aqu

a re

gia–

HF–

H2O

2PT

FEbo

mb

dige

stio

n, f

ollo

wed

by

10 m

in h

eatin

g w

ith H

3B

O3

ina

wat

er-b

ath

ET

AA

S (n

o m

odif

ier)

Res

ults

wer

e in

goo

d ag

reem

ent w

ith th

e ce

rtif

ied

valu

e fo

r C

r in

BC

R R

iver

Sed

imen

t. Sp

ike

reco

veri

es o

f 10

1–10

2% w

ere

obta

ined

95

Sedi

men

t an

dso

il sa

mpl

esN

iD

omes

tic o

ven

(110

0 W

)A

qua

regi

a–H

F–H

2O

2PT

FEbo

mb

dige

stio

n fo

r 12

min

(4

step

s) w

ith c

oolin

g be

twee

nea

ch s

tep.

Aft

er a

ddin

g H

3B

O3

the

sam

ple

is h

eate

d in

abo

iling

wat

er-b

ath

for

10 m

in

ET

AA

SG

ood

resu

lts w

ere

obta

ined

in

BC

R C

RM

143

R S

ewag

e Sl

udge

Am

ende

d So

il, B

CR

CR

M 3

20 R

iver

Sed

imen

t, N

IES

No.

2Po

nd

Sedi

men

t; C

anad

a C

entr

e fo

r M

iner

al

and

Ene

rgy

Tec

hnol

ogy

LK

SD 4

Lak

e Se

dim

ent;

MA

FF N

orth

Sea

San

dySe

dim

ent

CO

R 5

A/9

1 an

d G

eolo

gica

l Su

rvey

of

Japa

n JB

2T

hole

iitic

Bas

alt

97

Sedi

men

tsa

mpl

esA

sD

omes

tic o

ven

(700

W)

On-

line

pota

ssiu

m p

ersu

lfat

e–N

aOH

oxi

datio

n fo

llow

ing

HPL

C s

epar

atio

n of

As

spec

ies

(pri

or d

iges

tion

of s

ampl

es i

sne

cess

ary)

On-

line

anal

ysis

by

HG

–AA

SA

sV,

MM

A a

nd D

MA

spe

cies

wer

e de

term

ined

in

a se

dim

ent

extr

act.

No

CR

Ms

wer

e an

alys

ed10

7

Sedi

men

tsa

mpl

esH

gD

omes

tic o

ven

(750

W)

PTFE

bom

b H

NO

3–H

2SO

4–H

2O

2

dige

stio

n fo

r 4

min

fol

low

ing

pre-

dige

stio

n ov

erni

ght

CV

-AA

SG

ood

resu

lts

wer

e ob

tain

ed

for

Hg

in

ME

SS-2

E

stua

rine

Sedi

men

t. Sp

ike

reco

veri

es o

f 91

–108

% w

ere

obta

ined

in

Riv

er M

erse

y se

dim

ent

sam

ples

112

Dus

t w

ipe

and

air

filte

rsPb

Dom

estic

ove

n (8

00 W

)T

eflo

n PF

A H

NO

3di

gest

ion

for

6m

in (

n=

12)

ET

AA

S R

ecov

erie

s of

96

–114

%

wer

e ob

tain

ed

for

the

NIO

SH

and

EL

PAT

wip

e sa

mpl

es. F

or a

ir f

ilter

sam

ples

, spi

ke r

ecov

erie

sof

94–

103%

wer

e ob

tain

ed

172

Soil

and

sedi

men

tsa

mpl

es

Cd,

Cu,

Pb

—O

pen

HN

O3–H

2O

2–a

qua

regi

a–H

F di

gest

ion

follo

win

gov

erni

ght

pre-

dige

stio

n

ET

AA

SG

ener

ally

low

res

ults

wer

e ob

tain

ed f

or B

CR

Cal

care

ous

Loa

mSo

il, R

iver

Sed

imen

t an

d N

BS

Urb

an P

artic

ulat

e M

atte

r12

8

Silic

ate

rock

sFe

oxi

datio

nst

ates

—H

F–H

2SO

4PT

FE b

omb

dige

stio

nun

der

Ar

atm

osph

ere

Abs

orba

nce

at 5

60 n

m o

fFe

III –

Tir

on c

ompl

exfo

llow

edsp

ectr

opho

tom

etri

cally

with

tim

e

FeO

and

Fe 2

O3

resu

lts w

ere

com

pare

d w

ith th

ose

from

the

stat

ico-

phen

anth

rolin

e m

etho

d17

3

Soils

and

cla

ysA

l, C

a, F

e, K

,M

g, M

n, N

a,P,

Si,

Ti

—H

F–aq

ua r

egia

Tef

lon

bom

bdi

gest

ion

for

10 m

inIC

P-A

ES

Gen

eral

ly g

ood

resu

lts w

ere

obta

ined

for

NIS

T S

RM

164

6E

stua

rine

Se

dim

ent,

SRM

27

8 O

bsid

ian

and

SRM

68

8B

asal

t

174

Analyst, July 1998, Vol. 123 121R

Tab

le 3

Mic

row

ave

dige

stio

n pr

oced

ures

for

wat

er a

nd w

aste

wat

er s

ampl

es

Mat

rix

Ele

men

tsM

icro

wav

e sy

stem

Dig

estio

n m

etho

dA

naly

sis

Tec

hniq

ueC

omm

ents

Ref

.

Wat

er s

ampl

esSe

IVan

d Se

VI

Prol

abo

Mic

rodi

gest

301

On-

line

mic

row

ave

assi

sted

HC

lpr

e-re

duct

ion

of S

eVIto

SeIV

On-

line

anal

ysis

by

FI–C

SV

SeV

Iw

as

calc

ulat

ed

as

the

diff

eren

ce

betw

een

the

SeIV

conc

entr

atio

n af

ter

pre-

redu

ctio

n an

d th

e in

itial

Se

IV

conc

entr

atio

n. F

or a

BC

R c

andi

date

wat

er s

ampl

e, re

sults

wer

elo

w

for

SeIV

and

ther

efor

e hi

gh

for

SeV

I . T

he

tota

l Se

conc

entr

atio

n w

as

how

ever

in

go

od

agre

emen

t w

ith

the

prop

osed

val

ue

10

Wat

er a

ndw

aste

wat

ersa

mpl

es

Hg

Prol

abo

Max

idig

est

On-

line

dige

stio

n of

sam

ples

prep

ared

in

H2SO

4–H

NO

3–

KM

nO4–K

2S 2

O8

with

HC

lca

rrie

r

FI–m

ercu

ry s

yste

mG

ener

ally

goo

d sp

ike

reco

veri

es w

ere

obta

ined

for

ino

rgan

ic a

ndm

ethy

lmer

cury

in

drin

king

wat

er a

nd w

aste

wat

er s

ampl

es13

8

Wat

er s

ampl

esSe

Prol

abo

Mic

rodi

gest

M30

1O

n-lin

e H

Br–

KB

rO3

pre-

trea

tmen

tof

SeV

Ito

SeIV

(30

sam

ples

h21)

On-

line

anal

ysis

by

HG

–AA

S T

otal

Se

w

as

dete

rmin

ed

follo

win

g ap

plic

atio

n of

m

icro

wav

een

ergy

to

the

sam

ple,

whe

reas

SeIV

was

det

erm

ined

in

itsab

senc

e. S

eVI

was

cal

cula

ted

by d

iffe

renc

e. N

o C

RM

s w

ere

anal

ysed

175

Wat

er s

ampl

esSe

Prol

abo

Mic

rodi

gest

M30

1O

n-lin

e H

Br–

KB

rO3

pre-

trea

tmen

tof

Se

follo

win

g H

PLC

sepa

ratio

n of

spe

cies

On-

line

anal

ysis

by

HG

–AA

ST

he d

eter

min

atio

n of

sel

enite

, se

lena

te a

nd s

elen

oam

ino

acid

s(s

elen

ocys

tine,

sel

enom

ethi

onin

e an

d se

leno

ethi

onin

e) i

n ur

ine

was

und

erta

ken

176

Wat

er s

ampl

esSe

Prol

abo

Mic

rodi

gest

301

On-

line

HC

l (6

m)

redu

ctio

n of

SeV

Ito

SeIV

On-

line

anal

ysis

by

HG

–AA

ST

he S

eVIco

ncen

trat

ion

was

cal

cula

ted

as t

he d

iffe

renc

e be

twee

nth

e to

tal

Se c

onte

nt (

mic

row

ave

on)

and

the

SeIV

cont

ent

(mic

row

ave

off)

. Goo

d re

sults

wer

e ob

tain

ed f

or N

IST

164

3cT

race

Ele

men

ts i

n W

ater

177

Wat

er s

ampl

esSe

Prol

abo

Mic

rodi

gest

301

On-

line

HC

l re

duct

ion

of S

eVIto

SeIV

follo

win

g H

PLC

sepa

ratio

n of

SeV

Ian

d Se

IV

On-

line

anal

ysis

by

HG

–AFS

Res

ults

wer

e in

goo

d ag

reem

ent

with

the

tot

al S

e co

nten

t of

NIS

T16

43c

Tra

ce E

lem

ents

in

Wat

er17

8

Wat

er s

ampl

esA

s, B

i, H

g, P

b,Sn

Prol

abo

Max

idig

est

MX

-350

On-

line

dige

stio

n of

sam

ples

mix

ed w

ith a

sui

tabl

e ox

idis

ing

agen

t (d

epen

dent

on

elem

ent)

FI–C

V-A

AS

and

HG

–AA

SG

ood

Bi

and

Hg

resu

lts w

ere

obta

ined

, al

thou

gh p

robl

ems

wer

eex

peri

ence

d fo

r A

s, P

b an

d Sn

det

erm

inat

ions

179,

180

Wat

er s

ampl

esH

gPr

olab

o M

axid

iges

tM

X-3

50O

n-lin

e K

BrO

3–K

Br

dige

stio

n (7

sam

ples

h2

1)

FI–C

V-A

AS

inam

alga

mat

ion

mod

eG

ood

reco

veri

es

wer

e ob

tain

ed

for

the

seve

n H

g sp

ecie

sin

vest

igat

ed. T

he r

esul

ts f

or 2

2 w

ater

sam

ples

wer

e in

acc

epta

ble

agre

emen

t w

ith t

hose

obt

aine

d fr

om a

n ex

tern

al l

abor

ator

y

181

Wat

er s

ampl

esT

otal

N a

nd P

CE

M M

DS-

81D

Tef

lon

bom

b po

tass

ium

per

sulf

ate

and

NaO

H d

iges

tion

for

45 m

in(n

=12

)

Col

orim

etri

c de

term

inat

ion

Goo

d re

cove

ries

wer

e ob

tain

ed f

or a

ll P

and

N c

ompo

unds

tes

ted

exce

pt

for

anim

oant

ipyr

ine

(60–

73%

).

Spik

e re

cove

ries

of

98.4

–105

.9%

wer

e ob

tain

ed i

n re

al s

ampl

es

182

Was

te w

ater

sam

ples

Tot

al P

CE

M M

DS-

81D

On-

line

HN

O3

dige

stio

n w

ith p

rior

addi

tion

of p

yrop

hosp

hata

se (

25sa

mpl

es h2

1)

Col

orim

etri

c de

tect

ion

ofm

olyb

denu

m b

lue

com

plex

Res

ults

wer

e in

goo

d ag

reem

ent

with

tho

se o

btai

ned

form

a b

atch

‘blo

ck’

dige

stio

n (3

h)

. C

ompl

ete

reco

veri

es

of

tetr

amet

a-,

trim

eta-

, or

tho-

an

d py

roph

osph

ate

as

orth

opho

spha

te

wer

eob

tain

ed

183

Wat

er s

ampl

esC

OD

Mile

ston

e M

LS

1200

On-

line

K2C

r 2O

7–H

2SO

4ox

idat

ion

(3 m

in)

FI–s

pect

roph

otom

etri

cde

tect

ion

Res

ults

wer

e in

goo

d ag

reem

ent

with

tho

se o

f th

e st

anda

rd C

OD

met

hod

for

a ra

nge

of w

ater

sam

ples

and

foo

d in

dust

ry w

aste

64

Wat

er s

ampl

esSe

Mile

ston

e M

LS-

1200

ME

GA

On-

line

KB

r–H

Cl

pre-

trea

tmen

t of

SeV

I , Se

IVan

d Se

-Met

,fo

llow

ing

sepe

ratio

n by

ani

on-

exch

ange

chr

omat

ogra

phy

HG

–AA

ST

he

sepe

ratio

n of

Se

IV,

SeV

Ian

d Se

-Met

w

as

dem

onst

rate

d;ho

wev

er, n

o C

RM

s w

ere

anal

ysed

184

Wat

er s

ampl

esA

sD

omes

tic o

ven

(700

W)

On-

line

pota

ssiu

m p

ersu

lfat

e–N

aOH

oxi

datio

n, f

ollo

win

gH

PLC

sep

arat

ion

of A

s sp

ecie

s

On-

line

anal

ysis

by

HG

–A

AS

AsII

I , A

sVan

d ar

seno

beta

ine

wer

e de

term

ined

in m

iner

al, s

ewag

ean

d ha

rbou

r se

a w

ater

sa

mpl

es

alth

ough

no

C

RM

s w

ere

anal

ysed

107

Wat

er, w

aste

wat

er a

ndse

wag

eef

flue

nts

Tot

al P

Dom

estic

ove

n (7

00 W

)O

n-lin

e po

tass

ium

per

oxod

isul

fate

dige

stio

nFI

–col

orim

etri

c de

tect

ion

of p

hosp

hom

olyb

denu

mbl

ue c

ompl

ex

Com

plet

e di

gest

ion

of a

ll P

com

poun

ds te

sted

was

ach

ieve

d, e

xcep

tfo

r co

nden

sed

phos

phat

es.

No

sign

ific

ant

diff

eren

ces

wer

eob

serv

ed b

etw

een

the

resu

lts o

f th

e on

-lin

e an

d ba

tch

met

hods

,al

thou

gh t

he f

orm

er h

ad a

sm

all

posi

tive

bias

185

Was

te w

ater

sam

ples

CO

DD

omes

tic o

ven

(662

W)

On-

line

oxid

atio

n of

sam

ple,

prev

ious

ly m

ixed

with

K2C

r 2O

7

(up

to 5

0 sa

mpl

es h2

1)

On-

line

FAA

S an

alys

is o

fun

oxid

ised

Cr

follo

win

gan

ion-

exch

ange

sepe

ratio

n

The

CO

D v

alue

s ob

tain

ed f

or 1

2 di

ffer

ent

orga

nic

com

poun

ds a

ndfo

r ur

ban

and

indu

stri

al

was

te

wat

er

sam

ples

w

ere

not

sign

ific

antly

di

ffer

ent

to

thos

e ob

tain

ed

by

a cl

osed

re

flux

met

hod

186

122R Analyst, July 1998, Vol. 123

Reid et al.187 described a method for the rapid cooling ofTeflon pressure vessels using liquid nitrogen. Cooling in themicrowave unit itself, although considerably decreasing reac-tion rates, was useful in some cases to prevent uncontrollableincreases in pressure. However, a more effective methodinvolved cooling, subsequent to or between heating cycles. Thisapproach saved considerable time and additionally preventedpressure build-up occurring after the microwave process hadceased, which could otherwise lead to venting of the vessel.

Open digestion techniques

Open digestion systems operate at atmospheric pressure and sodo not suffer from the problems associated with pressurebuild-up. However, they do require an effective fume removalsystem. Most open vessel work has been carried out usingmonomode (focused) microwave systems.10–28,136–140,175–181

Heating is more efficient than with conventional microwavedesigns (multimode) because the sample is placed within thewaveguide, and thus directly within the path of the microwaveenergy. The potential loss of volatile species is controlled bycondensation of vapours in a reflux column situated above thesample flask. The open vessel approach can generally accom-modate larger samples (up to 15 g) than the closed techniqueand allows the delivery of digestion reagents at any stage of theprocedure. The latter may be beneficial for the effectiveness ofthe digestion, and is a distinct advantage over closed methodswhere the addition of reagents cannot readily be achievedwithout cooling and opening the vessels. Also, the system canquickly and effectively evaporate to dryness, a particular

advantage for the removal of HF during the digestion ofgeological samples. Another advantage is that the power outputof the magnetron can be controlled more readily than fordomestic ovens. For example, at 50% power the output of themagnetron is actually reduced to 50% rather than pulsing on andoff to produce an overall mean of 50% power (see the previoussection). Direct temperature measurements and temperaturecontrol to follow a previously defined programme are alsopossible.188

A potential disadvantage of the open monomode system isthat only one sample can be digested at a time, although this canbe overcome by use of an autosampler unit with the ability torun up to 16 samples.189 A multicavity monomode system isalso available for the digestion of up to four samples for thedetermination of Kjedahl nitrogen.190 A more recent addition tothe commercial market is a two- or six-cavity open microwavedigestion unit with the ability to programme the power output/desired temperature to each sample independently.191 Anotherpoint for discussion is that many open digestion procedures, byvirtue of operating at atmospheric pressure, must use a highboiling-point acid, such as sulfuric acid, in order to decomposecompletely organic material in the sample. Many workersovercome the use of highly corrosive sulfuric acid by utilisingperchloric acid or hydrogen peroxide instead.

A less common approach is the use of conventionalmicrowave ovens87,109,128 for open digestions. Burguera et al.87

demonstrated that the digestion of biological samples could beeffectively achieved for 100 samples placed in polyethylenetest-tubes (covered with a Teflon sheet) in only 14 min.However, no comment was made as to the lifetime of theoven.

Table 4 Key to abbreviations used

Analysis Techniques Reference Material Suppliers

AFS Atomic fluorescence spectrometry BCR Community Bureau of ReferenceCIE Capillary ion electrophoresis CCRMP Canadian Certified Reference Materials ProjectCV-AAS Cold vapour atomic absorption spectrometry CGC Canadian Grain CommissionDCP-AES Direct current plasma atomic emission spectrometry ELPAT Environmental Lead Proficiency Analytical Testing ProgramDP-ASV Differential-pulse anodic stripping voltammetry IAEA International Atomic Energy AgencyDPP Differential-pulse polarography ISS/MMM Istituto Superiore di Sanita, Rome, ItalyETAAS Electrothermal atomic absorption spectrometry KRISS Korea Research Institute of Standards and ScienceFAAS Flame atomic absorption spectrometry MAFF Ministry of Agriculture, Fisheries and Food, UKFAES Flame atomic emission spectrometry NBS National Bureau of Standards, USAFANES Furnace atomic non-thermal excitation spectrometry NIES National Institute of Environmental StudiesFI Flow injection NIOSH National Institute for Occupational Safety and HealthHG–AAS Hydride generation atomic absorption spectrometry NIST National Institute of Standards and Technology, USAHPIC High-performance ion chromatography NRCC National Research Council of CanadaHPLC High-performance liquid chromatography NRCCRM National Research Centre for Certified Reference Materials,

BeijingIC Ion chromatographyUSGS United States Geological SurveyICP-AES Inductively coupled plasma atomic emission spectrometry

ICP-MS Inductively coupled plasma mass spectrometryOthersID Isotope dilution

COD Chemical oxygen demandIR Infrared spectrometryCRM Certified reference materialNAA Neutron activation analysisMW MicrowaveSW-CSV Square-wave cathodic stripping voltammetryREEs Rare earth elementsTLC Thin-layer chromatographyRM Reference materialTXRF Total reflection X-ray fluorescence spectrometry

XRF X-ray fluorescence spectrometry

Compounds

APDC Ammonium pyrrolidin-1-yldithioformateBPTH 1,5-Bis[phenyl-(2-pyridyl)methylene]thiocarbonohydrazideDPTH 1,5-Bis(di-2-pyridylmethylene)thiocarbonohydrazineDTPA Diethylenetriaminepentaacetic acidEDTA Ethylenediaminetetraacetic acidHIPT 2-Hydroxy-4-isopropylcycloheptatrienoneIBMK Isobutyl methyl ketonePSAA 2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-

amino)anilineTMAH Tetramethylammonium hydroxide

Analyst, July 1998, Vol. 123 123R

On-line digestion techniques

There is a growing trend towards the development of on-linemicrowave digestion and analysis techniques, for bothsolid22,24,32,35,36,54,83,84,86,88,89,93,94,98,138 and liq-uid10,21,107,138,1752181,1832186 samples. Such techniques canlead to considerable time savings compared with batchmicrowave digestions and thus the benefits over conventionaltechniques are even more impressive. However, for solidsamples it is usually necessary to prepare a slurry of the samplebefore analysis. This is undertaken to ensure effective sampletransport into the digestion manifold. Most workers havereported the necessity for further grinding of the sample,sometimes with the addition of surfactants,35,89 in order toproduce a stable slurry. Samples can then be digested in eithera continuous or stopped flow system for on-line analy-sis22,24,35,36,86,88,89,93,98,138 or collected for separate treat-ment.32,35,54,83,84,94 Hulsman et al.192 investigated the disper-sion behaviour of solid particles in flow injection analysis inorder to help achieve reproducible pre-treatment procedures.

On-line microwave digestion of slurries has been successfulfor the determination of Al, As, Cd, Cu, Co, Cr, Fe, Hg, Mg,Mn, Ni, Pb and Zn in biological, soil and sediment samples.However, incomplete digestion has been reported for coalsamples.35 It has also been noted that for some detectionsystems, e.g., flame atomic absorption spectrometry (FAAS),that the mass of sample required for trace analysis may beincompatible with the slurry approach.35,36 Other workers havereported blocking of the transfer lines for some samples,therefore necessitating a pre-digestion before on-line treat-ment.54 An alternative method to the slurry approach has beenreported by Legere and Salin,193 who proposed encasing thesample in a digestible capsule for easy transfer into the digestiontube. Once in place the reagents could be added, the tube sealedand the digestion allowed to continue in a fully automatedsystem. Torres et al.139 developed a microwave-assisted roboticmethod for the extraction of Cu, Fe and Zn from soil samples.The system was capable of the weighing, extraction, centrifuga-tion and transport of the sample to the flame atomic absorptionspectrometer.

In contrast to the problems associated with solids, watersamples are more compatible with the on-line digestion process.Techniques suitable for the determination of the chemicaloxygen demand (COD),64,186 total P,183,185 As,107 Bi179,180 andHg138,179–181 and the speciation of Se175–178,184 have beendeveloped. These procedures result in considerable time savingson the batch techniques, especially if the system can becombined with an autosampler. Open monomode (focused)microwave digestion systems are particularly suited to on-lineapplications, having been successfully used by a number ofworkers for this purpose.21,22,138,175–179,181

Chemometrics

Chemometrics and factorial designs78,142,143,159,160 have beenused to select the best digestion technique for a particularpurpose, i.e., to chose the best combination of reagents, reagentvolumes, digestion times and power settings. This is ofparticular value in a multi-element situation when no singledigestion procedure gives good results for all the elementsrequired and a method is needed to obtain the best overallperformance. In addition, Feinberg et al.67 related digestionprogrammes with the nature of the sample matrix using anempirical modelling approach. A preliminary study usingKjedahl nitrogen determinations in food samples to definereference digestion procedures was found to be very effectivefor precisely defined samples. However, for complex foods themodel needed further development.

Universal digestion procedures

This section discusses the use of microwave digestion systemsfor the digestion of biological, geological and water samples, inorder to identify potential ‘universal’ digestion procedures for aparticular matrix or element. Tables 5, 6 and 7 summarise thedifferent reagent combinations that have been used for thedetermination of different elements in biological, geologicaland water samples respectively.

Biological samples

Many papers have been published reporting the use ofmicrowave digestion procedures for biological samples10–135

(Table 1). A wide range of samples have been investigated, thediversity of which is nearly matched by the number of differentdigestion methods used. A wealth of different combinations ofacids and oxidising agents are commonly employed for thedetermination of different elements in biological samples(Table 5). Few trends seem to exist with good results beingobtained for the same element in the same matrix after digestionwith a range of different reagents. Conflicting evidence alsoexists as to the efficacy of the same reagent combination for thedigestion of a particular matrix.

For the determination of aluminium in biological samplesthere is disagreement as to whether digestion with HF isnecessary. In support is the work of Lajunen and Piispanen,39

who reported low Al recoveries in NIST Citrus Leaves and PineNeedles and IAEA Mixed Diet after a closed nitric–hydrochlo-ric acid digestion. Recoveries were improved by employingnitric and hydrofluoric acid in combination with hydrogenperoxide. Low recoveries were also obtained in BCR SpruceNeedles following a nitric acid–hydrogen peroxide digestion25

and in shellfish,83 total diet samples120 and NIST Apple andPeach Leaves80 following closed digestion procedures with justnitric acid. For marine biological tissue (NIST Oyster Tissue),closed digestion procedures with nitric and perchloric acid, andnitric acid and hydrogen peroxide, also resulted in low resultsfor Al.56 However, good results were again achieved by theaddition of hydrofluoric acid to the nitric acid and hydrogenperoxide digestion mixture.

Evidence also exists, however, to suggest that digestion withHF is unnecessary for some samples. For example, good resultshave been obtained for Al in NIST Total Diet116 and in NISTCitrus Leaves135 after a simple nitric acid digestion. Acombination of nitric acid and hydrogen peroxide was used forthe digestion of NIST Wheat Flour, although results for NISTRice Flour were slightly high.74 Recoveries were not increased,however, by the inclusion of HF in the procedure. We havereported the successful determination of aluminium in tealeaves following an open nitric and perchloric acid digestion,although low recoveries were obtained with nitric acid, aloneand in combination with hydrogen peroxide.20

Similar discrepancies exist for the determination of iron. Asimple nitric acid digestion was used successfully for thedetermination of iron in cocoa,33 IAEA Horse Kidney,34 NISTTotal Diet,116 NIST Bovine Liver,36,70,119 and NIES Mussel,36

Chlorella,36 Sargasso36 and Pepperbush36 samples. However,Mingorance et al.69 obtained low and imprecise results forbotanical samples using a similar method. A slight improve-ment was obtained with a nitric and hydrofluoric acid digestion,but the results were still outside the certified range. Good resultswere obtained with nitric acid and hydrogen peroxide for NISTTotal Diet and with nitric and perchloric acid for NIESPepperbush and Mussel samples.69 However, low results wereobtained following both procedures for the determination of Fein BCR Wholemeal Flour. A nitric acid and hydrogen peroxidedigestion was also employed by Burguera et al.87 to give goodresults for NBS Bovine Liver, but for BCR Bovine Muscle theresults were slightly high. Using a similar procedure, good

124R Analyst, July 1998, Vol. 123

Table 5 Reagents for the microwave digestion of biological samples

Samples Reagents used Elements determined Ref.Marine Biological Tissues HNO3 Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg,

Mn, Ni, Pb, Se, Sr, Zn23, 27, 29, 52, 58, 59, 60, 70, 74, 83, 84, 92,

100, 102, 114, 117, 135HNO3 with V2O5 catalyst As 113HNO3–H2O2 Ag, Al, As, B, Cd, Cr, Cu, Hg, Mg, Mn,

Ni, Pb, Se, Sr, Zn16, 17, 21, 25, 37, 54, 57, 62, 65, 66, 76,

112HNO3–HCl Ni 81, 82HNO3–H2SO4 As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, Sr,

Zn23

HNO3–HF Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn,Ni, Pb, Se, Sn, Th, Zn

54, 77

HNO3–HF–H2O2–H3BO3 Al 56HCl–HNO3–H2O2 Cd, Fe, Zn 25HNO3–HClO4 Co, Cu, Fe, Pb 79HCl–HNO3–HF Ca, Cu, Fe, Zn 78HNO3–H2SO4–H2O2 As, Hg, Se 22, 105, 106, 129HNO3–H2SO4–HNO3–H2O2 Hg 11, 27HNO3–HClO4–HCl–HF Ca, Cd, Co, Cu, Fe, Mg, Mn, Zn 19, 103, 125HNO3–H2SO4–H2O2–NH4EDTA Ca, Cd, Cu, Fe, K, Mg, Mn, P, Sr, Zn 19HNO3–H2O2–HF Si 75HCl–Br2/BrO3

2 Hg 22Aqua regia–HF–H2O2 Ni 97K2S2O8–NaOH As 21, 107TMAH Hg, methyl-Hg 28Methanolic KOH Hg, methyl-Hg 28

Other biological tissues HNO3 As, Ag, Cd, Co, Cu, Fe, Hg, Mg, Mn, Mo,Po, Pb, Rb, Se, V, Zn

27, 34, 35, 36, 70, 119, 124, 134

HNO3–HCl Ni, Pb 81, 88HNO3–HClO4 Cd, Cu, Pb, Se 79, 118, 122HNO3– H2O2 B, Bi, Ca, Cd, Co, Cs, Cu, Fe, Hg, K, Mg,

Mn, Mo, Na, P, Pb, Rb, Ru, S, Sb, Se,Sn, Sr, Tl, Zn

10, 12, 17, 18, 45, 50, 57, 67, 72, 87, 96, 99,128

HNO3–HClO4–HCl–HF Ca, Cu, Fe, Mg, Mn, Zn 103HNO3–H2SO4–H2O2 As 110HNO3–H2SO4–HNO3–H2O2 Hg 27HNO3–H2SO4–H2O2–NH4EDTA Ca, Cd, Cu, Fe, K, Mg, Mn, P, Sr, Zn 19HNO3–HF–H2O2–H3BO3 Al 56H2SO4–KI Sb 25Acetic acid SbIII 25

Botanical samples(terrestrial)

HNO3 Al, As, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr,Cu, Eu, Fe, Hg, K, La, Mg, Mn, Mo, Na,Ni, P, Pb, Po, Rb, S, Se, Sm, Sr, Tb, Te,Th, U, V, Zn

15, 32, 33, 35, 41, 47, 49, 71, 74, 80, 85, 89,90, 116, 119, 134, 135

HNO3–H2O2 Al, As, B, Ca, Cd, Ce, Cr, Co, Cu, Eu, Fe,K, Mg, Mn, Na, Ni, P, Pb, S, Se, Sm,Tb, 232Th, 238U, Zn

12, 13, 15, 17, 25, 31, 38, 40, 41, 45, 63, 72,73, 76, 93, 98, 99, 101, 116, 128

HNO3–HCl Ca, Co, Cu, Fe, K, Mg, Mn, Na, Ni, Pb,Zn

30, 39, 81, 82, 88, 116, 127

HNO3–HClO4 Al, Ba, Ca, Cd, Cu, Fe, K, Mg, Mn, P, Pb,S, Zn

20, 53, 79, 109, 121, 122

HNO3–HClO4–HCl–HF Ca, Cd, Cu, Fe, Mg, Mn, Pb, Zn 103, 104, 125HCl–HNO3–HF Ca, Fe 78HNO3–HF–H2O2 Al, Fe, Mg, Si 39, 130HNO3–HF–H2O2–H3BO3 As, Ba, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb,

Sb, Tl, V, Zn46

HNO3–HF–HClO4–HF Cr, Fe 71HNO3–H2SO4 Al, Ca, Cu, Fe, Mg, Na, Zn 116H2SO4–H2O2 Kjeldahl N 14HNO3–HF Ba, Ca, Mg, Mn, Zn 42HNO3 with V2O5 catalyst As, Cd, Cu, Fe, Pb, Se 91, 115HNO3–H2O2–HCl P 133HNO3–HF–H2O2–SiO2 Al, B, Ba, Ca, Cr, Cu, Fe, K, Mg, Mn, Na,

P, S, Sr, Zn55

Aqua regia–HF–H2O2 Ni 97Aqua regia–H2O2 Cr 95NaOH–H2O2 Br2 111

Botanical samples(marine)

HNO3 Cd, Fe, Mg 36

HNO3–H2O2 Co, Cr 101HNO3–HClO4–HCl–HF Cd, Cu, Pb 103, 125

Analyst, July 1998, Vol. 123 125R

results have been obtained for BCR Pig Kidney,128 BovineMuscle128 and Liver18,50 and NBS Citrus Leaves,128 PineNeedles128 and Wheat Flour.128 However, low iron recoverieshave been reported using the same reagent combination forNBS Orchard Leaves, Spinach Leaves and Bovine Liver,72

BCR Rye Grass,40 IAEA Hay40 and for fat-rich foods.13 For thelast samples, recoveries were improved by use of a closednitric–sulfuric–nitric acid digestion. Sulfuric acid has also beenused by Krushevska et al.19 in combination with nitric acid,hydrogen peroxide and NH4EDTA to give good results forNIES Mussel Tissue, IAEA Horse Kidney and NIST BovineLiver and Oyster Tissue. For NIST Citrus Leaves the use ofnitric and hydrochloric acid gave low recoveries for Fe, butgood results were obtained for a variety of other metals.30

A number of workers, however, have reported that to obtaincomplete iron recoveries, digestion with HF was necessary. Forexample, for the digestion of NIST Citrus Leaves, Lajunen andPiispanen39 found hydrogen peroxide, nitric and hydrofluoricacid to be more effective than a simple nitric and hydrochloricacid digestion. Park and Suh71 reported that a nitric aciddigestion was unsuitable for the determination of Fe and Cr inrice flour samples, but in combination with hydrofluoric andperchloric acids complete recoveries were obtained. A nitric,perchloric, hydrochloric and hydrofluoric acid digestion wassuccessfully developed by Kojima et al.103 for the determina-tion of iron in NIST Bovine Liver and NIES Pepperbush andMussel samples, although for NIES Tea Leaves the results wereslightly high. Sun et al.55 obtained complete recoveries for ironin NIST Pine Needles and Apple, Tomato and Peach Leavesfollowing digestion with nitric acid, hydrofluoric acid andhydrogen peroxide. Mohd et al.78 used a chemometricstechnique to select the best reagent combination for thedigestion of NRCC TORT-1 and NIST Pine Needles. Thechosen procedure involved digestion with hydrochloric, nitricand hydrofluoric acid in which the hydrochloric and nitric acidwere present in equal proportions rather than as aqua regia.

A number of different techniques for the determination ofselenium have also been suggested. Banuelos and Akohoue31

investigated a number of different reagent combinations withand without a pre-digestion stage. Using a simple nitric aciddigestion, a selenium recovery of only 23% was obtained forNIST Wheat Flour. Recoveries were improved to 80% after anitric acid and hydrogen peroxide digestion with a 4 h pre-digestion step (57% without pre-digestion). However, furtherheating or the addition of hydrochloric acid did not increase therecoveries. In another publication,70 the determination ofselenium in NIST Bovine Liver was successfully achieved bydigestion with nitric acid, but results for IAEA Fish Flesh werelow. Selenium determinations have also been successfullycarried out using open nitric acid and hydrogen peroxidedigestion procedures for BCR Lyophilised Pig Kidney,10 cerealreference materials15 and NIST Bovine Liver12 and MixedDiet12 samples. However, results for NIST Total Diet12 wereslightly low. Good results have also been obtained in closeddigestions using nitric acid and hydrogen peroxide for BCRMaize Leaves38 and lyophilised fish samples.37 An alternative

technique, for the digestion of NIST Bovine Liver, was offeredby Prasad et al.118 This involved a closed nitric acid digestion,followed by evaporation to dryness with perchloric acid toremove organics and analysis by square-wave cathodic strip-ping voltammetry. However, for analysis by hydride genera-tion–atomic absorption spectrometry (HG–AAS) a similarprocedure was found to be ineffective. This was also the casewhen phosphoric acid or potassium persulfate was added.106

Good results were obtained, however, for NIES Mussel Tissueby using nitric and sulfuric acid with hydrogen peroxide;105,106

for NRCC DORM-2 and DOLT-2 after digestion with nitric andhydrofluoric acid66 and by a semi-on-line nitric acid digestionmethod for NIST Oyster Tissue84.

For arsenic, good results have been obtained using a nitricacid digestion for BCR Cod Muscle,11 NIST Oyster Tissue,117

NIST Orchard Leaves,49 NIST Bovine Liver70 IAEA FishFlesh70 and NRCC DORM-1,52 although for NRCC TORT-1results were slightly high.52 Yusof et al.60 and Liu et al.23

obtained good results for TORT-1 using a similar digestionprocedure. A nitric acid digestion was also carried out byNavarro and co-workers,113,115 in combination with a catalystof V2O5, to obtain good results for BCR Mussel Tissue and NBSCitrus Leaves. A nitric acid and hydrogen peroxide digestionwas successfully employed for the digestion of NIST OysterTissue and Orchard Leaves,76 for NRCC TORT-1 and DORM-1,21 for BCR Maize Leaves38 and for BCR Spruce Needles,White Clover, Cod Muscle and Plankton samples.25 However,El Moll et al.129 required the use of a more vigorous multi-stepprocedure with nitric and sulfuric acid and hydrogen peroxidefor the open vessel digestion of a range of fish samples.Krushevska et al.19 also employed a mixture of nitric acid,sulfuric acid and hydrogen peroxide, but in combination withNH4EDTA, for a range of biological samples. Schramel andHasse79 reported that a nitric acid procedure was successful forthe digestion of NIST Orchard Leaves, although for thedetermination of arsenic in fish by HG–AAS a nitric, perchloricand sulfuric acid digestion was necessary, presumably to breakdown organoarsenic compounds in the sample. In the work ofEdwards et al.66 the very low recoveries obtained for As inmarine biological samples, following digestion with nitric acidand hydrogen peroxide and HG–AAS analysis, was attributed tothe incomplete breakdown of organoarsenicals. For analysis byHG–AAS, Mayer et al.110 found a nitric acid, sulfuric acid andhydrogen peroxide mixture to be successful for the determina-tion of As in NIST Bovine Liver. McLaren et al.77 developed anitric and hydrofluoric acid digestion followed by hot-plateevaporation to dryness and dissolution of the sample in nitricacid for the determination of a range of elements, includingarsenic, in NRCC DORM-2 and DOLT-2. For the determinationof As and Se sewage sludge51 by HG–AAS, digestion withnitric and sulfuric acid has been found to be the most effectiveprocedure. An alternative approach for the breakdown oforganoarsenic compounds is to undertake an on-line potassiumpersulfate–sodium hydroxide digestion.21,107 Speciation ofarsenic may then be achieved by the coupling of an HPLCcolumn to the system. Using the former system we have also

Table 5 Continued

Sewage sludge samples HNO3 Cd, Cr, Cu, Hg, Ni, Pb, Zn 24, 32, 44, 86HCl–HNO3 Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K,

Mg, Mn, Mo, Na, Ni, P, Pb, Sn, Ti, V,Zn

44, 123

HNO3–H2O2 Cu, Mn, Pb 93, 98HNO3–H2SO4 As, Se 51Aqua regia–H2O2 Cr 95Aqua regia–HF–H2O2 Ni 97Aqua regia–HF–H2O2–H3BO3 Cd 96K2Cr2O7–H2SO4 COD 64

126R Analyst, July 1998, Vol. 123

shown that the determination of total arsenic was possible byvirtue of an l-cysteine pre-reduction step.21

The more readily released elements from biological matricessuch as Cu and Zn have been determined after digestion with avast number of different reagents ranging from nitric acidalone19,23,29,33–36,40,41,49,60,70,91,98,119,126 and in combination

with hydrogen peroxide13,15,16,18,25,41,50,72,87,93,98,101,116 tocombinations of nitric, perchloric, hydrochloric and hydro-fluoric acids.103,122

Methods for the determination of mercury are, however,slightly in agreement, with many workers employing a closednitric acid digestion procedure. Good results have been obtained

Table 6 Reagents for the microwave digestion of geological samples

Samples Reagents used Elements determined Ref.

Sediments HNO3 Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mn,Ni, Pb, Zn

24, 85, 121, 141, 144, 148, 150, 162

HNO3–H2O2 Cd, Hg 140HCl–HNO3 As, Cd, Hg, Pb, Se 161, 162, 170HNO3–HF Al, Ca, Co, Cr, Cu, Fe, K, Mg, Na, Ni, Pb,

Rb, Sr, Ti, V, Zn143, 162, 164

HCl–HNO3–H2O2 As, Cd, Cr, Cu, Ni, Zn 25, 137H2SO4–HNO3–HCl As, Se 148HNO3–H2SO4–H2O2 Hg 22, 112HNO3–HClO4-HF As, Ba, Co, Cr, Cu, Ni, Nb, Pb, Rb, Sb, Sn,

Sr, Ta, Th, Tl, W, Zn, REEs 141, 145

HNO3–HCl–HF Al, As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg,Mn, Mo, Ni, Pb, S, Se, Th, Ti, U, V, Y,Zn, lanthanides

25, 54, 142, 147, 158, 159, 160, 161, 163,165

HNO3–HF–HNO3 Cd, Cr, Cu, Ni, Pb, Sb, Sn, Th 78HNO3–HClO4–HF–HCl As 137HNO3–HF–H2O2–H3BO3 Ag, Al, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Hg,

Li, Mg, Mn, Mo, Ni, Pb, Sb, Sn, Sr, Th,Ti, Tl, U, V, Zn

45, 169

HF–aqua regia Al, Ca, Fe, K, Mg, Mn, Na, P, Si, Ti 174Aqua regia–KMnO4 Hg 138Aqua regia–HF–H2O2 Cr, Ni 95, 97HCl–Br2/BrO3

2 Hg 22

Rocks/minerals HNO3 Co, Cr, Cu, Mn, Mo, Ni, V 141HCl Fe 72HNO3–HF Co, Cr, Cu, Ni, Pb, Zn 143HCl–HF Al, K, Mg, Si 72HNO3–HClO4–HF Al, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Dy,

Er, Eu, Fe, Ga, Gd, Ge, K, Hf, Ho, In,La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd,Ni, Nb, Pr, Pb, Rb, Sb, Sc, Sm, Sn, Sr,Ta, Tb, Th, Ti, Tl, Tm, U, V, W, Y, Yb,Zn, Zr, REEs

151, 157

HF–H2SO4 Fe 173HNO3–H2SO4–K2Cr2O7 Os 149HF–HNO3–HCl As, Se, Th, U, Y, lanthanides 38, 165HNO3–HCl–HF–HClO4 Au, Ir, Pb, Pt, Rh, Ru 152Aqua regia–HF–H2O2 Ni 97HF–aqua regia Al, Ca, Fe, K, Mg, Mn, Na, P, Si, Ti 174

Soil HNO3 Hg 24, 136HNO3–H2O2 As, Cd, Cu, Ni, Pb, Zn 25,77HNO3–H2SO4 As 51HCl Hg 136HNO3–H2O2–HF Si 19HNO3–HF–H2O2–H3BO3 Al, Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Li,

Mg, Mn, Mo, Ni, Pb, Sb, Sn, Sr, Th, Ti,Tl, U, V, Zn

169

Aqua regia Hg 136Aqua regia–HF–H2O2 Ni 97

Dust, ashes and airborneparticulate matter

HNO3 Cd, Hg, Pb 32, 162, 168, 172HNO3–H2O2 As 77HNO3–H2SO4 As, Se 171HCl–HNO3 Cd, Pb 162HNO3–HF Cd, Pb 162HNO3–HCl–HF Al, Ba, Ca, Cr, Cu, Fe, Mg, Mg, Ni, Ti, V,

Zn147

HNO3–HClO4–HF Al, As, Ba, Cd, Cr, Cu, Fe, K, Mg, Mn, Na,Ni, Pb, S, Sb, V, Zn

153, 154, 155, 156, 166

HNO3–HF–H2O2–H3BO3 Al, Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Li,Mg, Mn, Mo, Ni, Pb, Sb, Sn, Sr, Th, Ti,Tl, U, V, Zn

169

Coal HNO3–H2O2–HF–HCl REEs

Analyst, July 1998, Vol. 123 127R

for BCR Pig Kidney,27,134 Mussel Tissue114 and Cod Muscle92

NIST Citrus Leaves,85 Pine Needles85 and Albacore Tuna,59

IAEA Fish Tissue27 and NRCC TORT-162 using this procedure.However, a number of workers have reported the use of strongoxidising reagents such as sulfuric acid and hydrogen peroxidefor the determination of mercury using open22,27 and closedmicrowave digestion systems.62,66,111 An on-line system devel-oped in our own studies for the determination of Hg inbiological and sediment samples has been reported.22 Thesystem was suitable for the analysis of samples containingorganomercury compounds by the utilisation of a bromide–bromate oxidation reaction. For the speciation of mercury,Tseng et al.28 have developed an open focused microwaveassisted extraction procedure for analysis by HG–CT–GC–ETAAS.

Geological samples

Less work has been carried out for the digestion of geologicalsamples than for biological samples, although a wide range ofmatrices have been digested by a number of different digestionprocedures (see Tables 2 and 6). Included are sediment, soil,rock, coal, ash and dust samples.

For the determination of some elements simple nitric orhydrochloric acid digestions will suffice for some samples. Forexample, good Fe recoveries in Fe ore samples were obtainedusing a simple hydrochloric acid digestion, but for limestonesamples the additional use of hydrofluoric acid was required.72

Lead in dust wipe and air filters172 has been determined after anitric acid digestion. Mercury was also determined using asimilar procedure in NIES Pond Sediment,121 baghouse dust168

and NIST SRM Estuarine Sediment and Buffalo River Sedi-ment.148 However, other workers reported high results for NISTBuffalo Sediment141 and slightly low results for NIST RiverSediment.85 Following both an open and closed nitric aciddigestion procedure, results were also low for mercury in NISTMontana Soil.136 However good results were obtained for Hg inNRCC PACS-1, IAEA-356 and BCR S19 sediment samplesfollowing open digestion with nitric acid.140 Morales-Rubioet al.24 have found the on-line digestion of slurries prepared innitric acid to be successful for the determination of Hg in soiland sediment samples. An alternative system for the determina-tion of mercury has been proposed by Hanna and McIntosh.138

Sediment slurries, prepared in aqua regia and potassiumpermanganate, were digested on-line for analysis in a flowinjection mercury system. In addition, an on-line systememploying a bromide–bromate oxidation reaction has beendeveloped in our studies for the determination of mercury insediment samples.22

Feng and Barratt162 observed no significant differencesbetween the results obtained after digestion with nitric acid,with hydrochloric and nitric acid or with nitric and hydrofluoric

acid for the determination of Cd and Pb in BCR City WasteIncineration Ash, BCR River Sediment and in NBS UrbanParticulate Matter. However, using a nitric acid and hydrogenperoxide digestion, low Cu and Pb (but good Cd) results wereobtained in the last two samples and in BCR Calcareous LoamSoil by Chakraborti et al.128 The results were improved byemploying an extra heating step with aqua regia and HF. Goodresults for cadmium in sediment samples were obtainedfollowing digestion with just nitric acid.144 A nitric aciddigestion was also employed by Averitt and Wallace141 toobtain good results for As, Cd, Co, Cu, Ni and Pb in NISTBuffalo River Sediment, although the Ba, Cr, Mn, Sb, V and Znresults were low and Hg results were high. Barium, Hg and Vresults were improved using a nitric, perchloric, hydrofluoricacid digestion procedure, but Cr was still low and Zn and Sbhigh. Marr et al.146 reported a benefit from the addition of HF toan aqua regia digestion for the analysis of the sediments NRCCMESS-1 and PACS-1, but again the results for Cr and Mn werelow.

In environmental analysis, it is often useful to acquireinformation on the bioavailable rather than the total elementspresent. This can often be achieved by using a mild leachingprocedure. Paudyn and Smith147 carried out such a procedurefor NRCC MESS-1 and PACS-1 and NIST Coal Fly Ash. Thiswork also demonstrated how the digestion conditions requiredfor the total release of different elements varies from sample tosample. For example, complete recoveries of Mn were obtainedfor NIST Fly Ash, compared with only 63% for MESS-1sediment. Total recoveries were also obtained for Cu and Zn inall samples whereas for other elements recoveries were muchlower, e.g., 35–60% for chromium, thus warranting a morevigorous digestion procedure.

Low Cr and Al values were obtained for NRCC BCSS-1sediment following an on-line hydrofluoric, nitric and hydro-chloric acid digestion, although recoveries for As, Cd, Co, Cu,Fe, Mn, Ni, Pb and Zn were good. Using a similar combinationof reagents, good results were obtained for Cr in NRCC BCSS-1, although the results for NIES No. 2 Pond Sediment were low.Following disappointing results using a number of medium- andhigh-pressure digestion procedures for Cr in NRCC BCSS-1,Liu et al.145 concluded that no acid dissolution procedures wereadequate for this sample. Low Al and Cr results have also beenreported for NIST Urban Particulate Matter after digestion withnitric, perchloric and hydrofluoric acids, however results for As,Cd, Cu, Fe, Mg, Ni, S, Sb and Zn were good.166 Completerecoveries of Cr have been obtained for NIST Fly Ash, NRCCMESS-1 and PACS-1 following a nitric, hydrochloric andhydrofluoric acid digestion.147 Good recoveries were alsoobtained for Cr in Mississippi River delta sediment following anitric and hydrofluoric acid digestion77 and by an aqua regia,hydrofluoric acid and hydrogen peroxide digestion for BCRRiver Sediment.95. However, good Cr recoveries were obtainedwithout the use of HF following an open hydrochloric, nitricacid and hydrogen peroxide digestion (and in a closedhydrochloric, nitric and hydrofluoric acid digestion) in BCREstuarine Sediment.132 Good As, Cd, Cu, Ni and Zn recoverieswere also obtained, although Hg and Pb levels were high.Totland et al.151,152 also employed HF in combination withnitric and perchloric acid for the successful digestion of ninerock and sediment samples.

For the determination of As and Se in soil51 and in coal flyash171 by HG–AAS, digestion with nitric and sulfuric acids hasbeen found to be the most effective procedure. Lasztity et al.76

employed a nitric acid and hydrogen peroxide digestion for thedetermination of As in NIST Urban Particulate Matter andIAEA Soil 7, whereas a nitric, hydrochloric and hydrofluoricacid digestion was successfully employed by Jimenez de Blaset al.38 for the determination of As in soil samples. Thedetermination of As in airborne particulate matter has been

Table 7 Reagents for the microwave digestion of water and waste watersamples

Reagents usedElementsdetermined Ref.

K2S2O8 Total P 185K2S2O8–NaOH As, total P and N 107, 182H2SO4–HNO3–KMnO4–K2SO8 Hg 138HNO3 and pyrophosphatase Total P 183KBrO3–KBr Bi, Hg 179, 180, 181KBrO3–HBr Se 175, 176HCl Se 10, 177, 178K2Cr2O7–H2SO4 COD 64, 186KBr–HCl Se 184

128R Analyst, July 1998, Vol. 123

undertaken by digestion with nitric, hydrofluoric and perchloricacids156.

For the determination of rare earth elements in coal, Watkinset al.167 employed a closed nitric acid, hydrogen peroxide,hydrofluoric and hydrochloric acid digestion. Sen Gupta andBertrand165 developed a hydrofluoric, nitric and hydrochloricacid digestion for the determination of Th, U, Y and thelanthanides in a large number of sediment and rock samples.

The use of a chemometrics technique for the selection of thebest technique for the determination of Co, Cu, Mn, Pb and Znin NBS Buffalo River Sediment was reported by Kokot et al.142

A digestion procedure with hydrofluoric, nitric and hydrochlo-ric digestion was selected, whereas for Co, Cr, Cu, Ni, Pb andZn a nitric and hydrofluoric acid digestion was found to be mosteffective.143. A hydrofluoric, hydrochloric and nitric aciddigestion procedure was selected by an orthogonal array designfor the digestion of sediment samples.158,160

Water Samples

Relatively few publications have reported the application ofmicrowave digestion to the determination of elements in watersamples (see Table 3).10,107,138,175–185 Benson et al.185 success-fully employed an on-line potassium persulfate digestion for thedetermination of total phosphorus, although incomplete diges-tion of condensed phosphates was observed. A similar digestionprocedure, but in batch mode, was applied for the determinationof total phosphorus and nitrogen by Johnes and Heathwaite.182

Complete recoveries for phosphorus were obtained but fornitrogen the breakdown of aminoantipyrine was incomplete.The determination of phosphorus was also carried out using anitric acid digestion with prior addition of pyrophosphate togive complete recoveries of tetrameta-, trimeta-, ortho- andpyrophosphate.183 Arsenic speciation has been achieved by on-line HPLC separation followed by a potassium persulfate andsodium hydroxide microwave digestion and analysis by HG–AAS.107 Pitts et al.177 developed an on-line microwavereduction system for the conversion of SeVI to SeIV prior toanalysis by HG–AFS. In a subsequent study by the sameauthors, the system was used for the speciation of SeVI and SeIV

following separation by HPLC.178 A similar system for the pre-reduction of SeVI to SeIV, but for analysis by FI–CSV, wasreported by Bryce et al.10 The determination of Se has also beenaddressed using on-line HBr–KBrO3 pre-reduction methods,developed by Gonzalez LaFuente et al.175 and coupled withHPLC separation by Marchante-Gayon et al.176 Ellend et al.184

have also developed an on-line separation and pre-treatmentmethod for the speciation of Se. For the determination ofmercury by CV-AAS, digestion with KBrO3–KBr is commonlyused. Welz et al.181 developed an on-line system for Hg and Bi,although problems were encountered in the determination ofAs, Pb and Sn. As described previously, a system for the on-linedetermination of Hg in sediments, water and waste watersamples was proposed by Hanna and McIntosh.138 For CODdeterminations, Balconi et al.64 and Cuesta et al.186 developedon-line methods employing a K2Cr2O7–H2SO4 digestion.

Conclusions

Biological samples consist of a complex mixture of carbohy-drates, proteins and lipids and so are not completely soluble inwater or organic solvents. Before analysis it is thereforenecessary to decompose the organic matter and release themetals from the sample matrix. The majority of the digestionprocedures used to date involve the initial use of strongoxidising agents such as nitric acid to decompose the organicmatrix of the sample. Many elements are then liberated assoluble nitrate salts. Other acids can be employed to break downthe sample further, according to the elements that need to be

determined and the analysis technique chosen. For example,hydrochloric acid is a good solvent for many metal oxides, formetals that are oxidised more easily than hydrogen and for someorganometallic compounds. The use of hydrofluoric acid isnecessary for the determination of a number of elements whichare associated with siliceous minerals.

For the determination of iron and aluminium in biologicalsamples, a wide variety of reagents have been successfullyemployed. For the former, digestions with nitric acid alone andin combination with hydrogen peroxide are very common andgenerally effective for the digestion of biological samples.However, the requirement for HF during the digestion of somebotanical samples has been reported. For the determination ofaluminium many workers have reported that the low resultsgenerated from digestion with just nitric acid or nitric acid andhydrogen peroxide can be improved by the addition of HF.However other workers have found this step unnecessary.Therefore, no steadfast rules regarding the need for HF duringthe determination of Al and Fe can be made, since it depends onthe exact sample type and the amount of siliceous materialpresent. The determination of Al is also hindered by highbackground levels, which can be prohibitive for trace analysis.Hence measures to control background contamination, inaddition to the preparation of sample blanks, should be routinelyadopted to minimise this problem.

For the determination of arsenic, digestion with nitric acidmay be used successfully in many cases, although for theanalysis of fish samples by HG–AAS more vigorous conditionsare usually required. Sulfuric acid is often employed to breakdown organoarsenic compounds which are not reduced and thusnot hydride forming upon reaction with sodium borohydride.Similar findings have also been observed for the determinationof Hg and Se. For the latter, nitric acid and hydrogen peroxidedigestions have been used successfully to replace the conven-tional nitric and perchloric acid and sulfuric acid procedures.However, when analysis by hydride generation is desired,sulfuric acid is still required to break down the more resistantorganoselenium compounds. For the less strongly boundelements in biological materials, such as Cu and Zn, thedigestion procedure is less critical with a wide range of differentreagent combinations giving good results.

The wide range of sample compositions represented bygeological materials preclude the use of any single digestionprocedure. For example, sediment samples consist of acombination of different materials, e.g., clay, organic material,siliceous and other minerals, and are therefore one of the mostdifficult sample matrices to digest. Hence in many cases, toattain complete digestion the use of HF is necessary todecompose resistant minerals, in addition to strong oxidisingreagents such as nitric acid and sometimes perchloric acid tobreak down organic matter. In the literature there is evidence tosuggest that a number of elements such as Cd, Cu, Hg, Pb andZn can be easily released after digestion with just nitric orhydrochloric acid. This is because in many cases they are sorbedon clay minerals or are in other readily decomposed phases,rather than within the resistant framework-lattice silicates.However, other elements are more strongly bound, either as partof resistant minerals or associated with other minerals, and so insuch cases the use of HF may be required. For example, some Crbearing minerals, notably chromite, are very difficult todecompose even with the use of HF–HClO4 under pressure,although complete Cr recoveries have been reported without theuse of HF. The need for HF is therefore very much dependent onthe nature of the minerals present in the samples. Because realsamples will vary in composition from that of the certifiedreference materials used for validation of a procedure, it wouldseem prudent to suggest that for the determination of all but themost weakly bound elements in sediments, digestion with HF isrecommended.

Analyst, July 1998, Vol. 123 129R

The digestion reagents required for the efficient digestion ofa particular sample type are very much dependent on the exactsample matrix and the elements to be determined. Excludingwater samples there is generally little agreement in theliterature, with often conflicting evidence as to which reagentcombinations are most effective for the same matrix. This mayreflect the fact that the digestion is influenced by factors otherthan just the choice of reagents, e.g., the relative proportions ofeach reagent, heating times and the pressure and temperaturereached during the procedure. In many cases good results for thesame matrix have been reported by a number of differentmethods. In addition, the literature suggests that no standarddigestion procedures can be employed for the determination ofa specified element in all samples of the same type, e.g., Fe inall biological samples, or for the determination of all theelements in a particular sample, e.g., all the elements in musseltissue. Therefore, it may not be justified to extrapolate atechnique designed for the determination of just a few elementsto a multi-element determination.

The choice of sample preparation method may, however, beinfluenced by a number of practical considerations in additionto the type of sample and elements to be determined. These mayinclude the number of samples to be analysed, method ofanalysis, safety aspects, capital and operating costs of equip-ment, operator skill and the degree of accuracy and precisionrequired. The method of final analysis is an important factor,influencing the extent of the digestion required, e.g., forelectroanalytical techniques complete breakdown of the organiccomponents is necessary, whereas ICP-AES can toleratedissolved solid contents of up to 1–2%. Also, the addition ofcertain reagents during the reaction can be considered. Forexample, the addition of boric acid for HF neutralisation maycause the final solution to possess a high solids content, whichcan give problems in sample introduction systems in addition toincreasing the background signal and thus degrading sensitivity.ICP-MS suffers from a number of interferences, particularlypolyatomic ion interferences. Hence the presence of a numberof acids, including hydrochloric and sulfuric acid, in the finalsolution is not recommended for the determination of someelements. Therefore, adapting a digestion method for analysisby a different technique to that originally intended may notprove successful.

When considering the speed of a particular procedure, it is notjust the time for the actual digestion that should be considered.Other factors should also be taken into account, e.g., samplepreparation before analysis, including grinding and slurryformation; pre-digestion and cooling times, including thosenecessary between reagent additions/heating cycles; and thewashing of digestion vessels. These factors are often over-looked.

A standard method of validating a procedure is to use asuitable certified reference material. However, as discussedpreviously, there seems to be a lack of consistency in the‘grading’ of these results. Often results are classed as ‘good’even though they do not lie within the uncertainty limits of thecertified values.

As mentioned above, it is not just digestion procedures whichlend themselves to automation, but also the choice of digestionmethod. Chemometrics and factorial designs have been usedeffectively to help choose the best digestion procedure for aparticular purpose. Models have also been developed to predictdigestion methods depending on the composition of the sampleof interest. This undoubtedly is a useful step forward, especiallyto predict digestion conditions for new samples.

For batch digestions, many closed digestion procedures aredeveloped in terms of heating at a particular power setting for acertain period of time, usually optimised to maximise energyinput without causing venting of the vessels. These proceduresare therefore operational, i.e., specific to the particular micro-

wave system and bomb design used. Adaptation for use in adifferent laboratory may not be straightforward unless the sameequipment is used, as re-optimisation of the original powersettings and heating times may be necessary. The optimumpower and time settings may also vary considerably accordingto the exact nature of the sample owing to the amount of organicmatter present, which influences the amount of gaseousproducts evolved during the reaction.

It has been shown that direct temperature and pressuremeasurements during the course of the digestion are possible.Such measurements can then be fed to a computer controllingthe magnetron to achieve a pre-set temperature or pressureprogramme. This technology offers the potential to produce farmore reproducible and controllable procedures, reducing thepossibility of venting of digestion vessels. In closed systems italso enables the system to be operated to its full digestionpotential, i.e., at its maximum pressure level without venting,regardless of the exact level of organic matter. Following thisapproach, digestion procedures can be transferred far moreeasily between similar samples and between different workers,and could potentially lead to the establishment of standarddigestion procedures, in addition to improving the overall safetyof this technique.

There has been a growing trend in recent years towards thedevelopment of fully automated on-line microwave digestionand analysis techniques. This area is well suited to water andwaste water samples, of which a large number are routinelyanalysed in many laboratories. Open monomode (focused)systems have been found to be particularly useful for on-lineapplications. Further developments are likely through both theadaptation of standard batch digestion methods to on-lineapplications and in the development of new chemistries suitedto the on-line approach. The digestion of solids is complicatedby the method of introducing the sample into the system.Introduction in the form of a slurry is one approach; however,the determination of low levels of analyte may be problematicowing to limitations in the maximum stable slurry concentra-tion. However, despite the initial problems encountered withon-line microwave digestion systems for solid samples, goodresults have been obtained for a number of biological andgeological materials. This approach to sample digestion wouldseem to offer much potential for further development and couldresult in dramatic time savings over batch microwave andconventional digestion techniques.

The authors thank Prolabo, Paris, France, for supporting theirstudies in the area of microwave digestion.

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Paper 8/00776DReceived January 28, 1998

Accepted April 7, 1998

Analyst, July 1998, Vol. 123 133R