AECL-5311

ATOMIC ENERGY WSm L'ENERGIE ATOMIQUEOF CANADA LIMITED XjBBf DU CANADA UMITEE

AN AUTOMATED WAVELENGTH SELECTIOII

FOR FLAME SPECTROSCOPY

by

M. HURTEAU, J.P. MISLAN and R.W. ASHIEY

Chalk River Nuclear Laboratories

Ch~alk River, Ontario

January 1976

\\ AUTOMVI'I.n WAVFiLI-NfTIl Sf-.LF.(-rin\

Fi.VF SPI'f"T

M. Hurteau, .I.''. Mislan and '} .'<. \shlov

General Chemistry BranchAtomic Energy of Canada LimitedChalk River Nuclear Laboratories

Chalk River, Ontario, CanadaKO.J 1.T0

.Tanuarv 1976

-5311

Sélection automatique de longueurs d'ondes pour la spectroscopie â flamme

par

M. Hurteau, J.P. Mislan et R.W. Ashley

Résumé

On décr i t un simple système de programmation électromécanique

pouvant être employé avec un spectrophotomëtre a flamme. On i l l us t re

son application pour l 'analyse séquentielle automatisée à éléments

mult iples. La reproduct ib i l i té des réglages de longueur d'onde esto

à ±0.5 A. La précision et la sensib i l i té sont au moins aussi bonnes

que celles obtenues pour la détermination d'éléments simples.

L'Energie Atomique du Canada, LimitéeLaboratoires Nucléaires de Chalk River

Chalk River, OntarioKOJ 1J0

Janvier 1976

AECL-5311

AN AUTOMAT P. D WAVELENGTH SELECTION FOR

FLAME SPF.CTROSCOPY

''. Hurteau. I.P. Mislan and R.W. Ashley

Abstract

A simple electro-mechanical programming system is

described for use with a flame spectrophctometer. Its

application for automated sequential multi-element analysis

is illustrated. Reproducitility of wavelength settings areo

within .tO.5 A. Precision and sensitivities are at least

as good as those obtained for single element determinations. 1 •'

General Chemistry BranchAtomic Energy of Canada LimitedChalk River Nuclear LaboratoriesChalk River, Ontario, Canada

KOJ 1J0

January 1976

AECL-5311

A\ A U T O M A T E D KAVlil.HNCVTII Si.lJCl ION FOR

FI.AMC SIM.CTROSCOI'Y

^. M-.irtc-i'i, '.;\ "•-•. I/in a n d R . K . A s h l e y

INTRODUCTION

Two general approaches, which invilvv either < i'v.il t ar."<vtj ~

or ^euuential wrivel enet h seh-ctinn, can !-e u<eii for aut'^iat i c

mul t i - element ^latne snoc trope tr i c analv^is.

In the simultaneous-read ing instrument, individual photo-

multiplier detectors are positioned on the focal plane of the

instrument to monitor the intensity of a spectral line for

each elemei.i" of interest fi). These instruments are complex

and costly, and hence have enjoyed popularity only for

analyses where optical filters can be substituted for

diffraction gratings. Sullivan and Walsh (2) have shown that

simultaneous multi-element analysis can be achieved by using

special hollow cathodes as 'resonance' monochromators. This

arrangement permits monitoring of at least four elements.

Despite its apparent usefulness, this technique has not gained

wide acceptance.

Sequential wavelength selection can be simply achieved

by repetitive scanning of selected wavelength regions (3,8).

This approach has been reported by Dawson et al. (3). In-

terference filters mounted in a rotating wheel have been used

successfully for sequential wavelength selection in atomic

fluorescence spectroscopy (AFS) (4). This annroach is not generally

applicable to atomic absorption or atomic emission spectroscopy

because of high resolution requirements. Malmstadt and Cordos (5)

have reported the development of a programmable monochromator

which selects desired wavelengths via a computer actuated

stepping motor attached to the wavelength drive mechanism of

a commercial instrument. Results have been reported for multi-

element AFS.

We have developed a relatively simple and inexpensive

electro-mechanical programming module. Its usefulness for

sequential multi-element flame emission spectroscopy is described

in this report.

WAVELENGTH SELECTOR (shown in Fig. 1)

The wavelength selector is basically a 16.5 cm (6.5 in) diameter

hollow aluminum cylinder with a spiral groove (16 meters)

machined in the outer surface. It is rotated at 10 rpm by

a 28 rpm motor (Bodine Type N-1D) via a reduction gear. This

wavelength selector is interfaced to the monochromator of a

Techtron AA-5 spectrometer through a Techtron scanning attach-

ment (Model 70). Another gear train steps up rotation of this

scanner to 100 rpm. When continuous spectral line scanning is

desired the selector m e c h a n i s m can be quickly disengaged.

Adjustable a c t u a t o r s , shown in ':ig. 1, are positioned in

the groove of the wavelength selector at positions corresponding

to desired wavelengths. These actuators trip a tracking micro

switch, which moves along a threaded rod in synchronization with

the drum. This stops the motor and energizes a brake mechanism

which minimizes ger.r backlash.

Alignment of the wavelength selector for desired wavelengths

is done as follows:

d ) Disengage the wave l e n g t h selector from the scanning unit.

c

f 2 ̂ Set the monochromator 200 A below the Invest wavelcngt!.

des i red.

(3) With the motor disengaged, rotate the wavelength selector

to "start" posit:..' R -engage the wavelength selector

and scanning unit.

(4) Rotate the selector cylinder until the monochromator wave-

length indicator reads the lowest wavelength reauired in

the analysis.

(5) Install an actuator to trip the micro switch at this

point.

This procedure is repeated for all wavelengths required.

SYSTEM PROGRAMMING

All functions in the system are controlled automatically by

- 4 -

a Cramer multiple-pole program timer (Model 540} (Fig. 2).

The electrical circuits are shown in Figs. 3 and 4.

At the start of a cycle the Cramer programmer, via a

5-pole relay (Potter and Brumfield Model #KBP20AG), activates

the event marker pen indicating start of cycle, turns on the

recorder drive and opens the shutter. After 10 seconds, rotation

of the wavelength selector drum starts and the shutter closes

to record instrument background. Drum rotation continues

until the first pre-positioned actuator on the drum trips the

tracking switch. At this point a brake, controlled through

the tracking switch, locks the drum in position and the shutter

opens. Concurrently, an automatic sampler cycle is started

and solvent background and signal from the sample are recorded.

After about 1.5 minutes, the appropriate cam in the Cramer pro-

grammer overrides the tracking switch to allow the drum

rotation to continue. This operation is repeated for all the

spectral lines pre-selected. After the last emission line

signal has been recorded, the programmer actuates a relay to

return the wavelength selector drum to the starting position

and the equipment is ready for the next sample. Analysis time

is about 2 minutes per element.

A typical recorder trace is shown in Fig. 5.

RHSULTS

All flame emission measurements were made using a \2O

acetylene flame, slit width of 300 pm (band pass ',1.0 mn),

burner height of 8 mm, nebulization rate of -.5 ml/min, R-213

photomuJ tiplier.

Conditions chosen for emission measurements were a com-

promise of the optimum conditions determined for the individual

elements.

The system described has been tested for 1) wavelength

selection, 2) precision and 3) sensitivity.

[1) Wavelength Selection

With the wavelength selector directly coupled to the

Techtron scanning attachment,the wavelength range covered is

3000 A. This range can be increased by installation of a

suitable gear train between the selector and scanning attachment to

increase the rotation speed of the monochromator relative to the

selector. A two-fold increase (giving a wavelength range of

6000 A) is considered to be the maximum required.

The maximum resolution of the wavelength selector is

governed by the minimum spacing of the actuators which is attain-

able. In this system this was approximately 50 A.

The reproducibility of the wavelength selection was checked

by operating the instrument as described for 5 element selection

over 200 cycles. The selected wavelengths were recorded from

- 6 -

the d i g i t a l wavelength counter of the spec t rometer . The r e -

p r o d u c i b i l i t y observed was within ±0.S A.

(2) P rec i s ion

Standard solutions were prepav:d containing five elements

in the following concentrations: Cu = 30 yg/ml, Fe = 55 ug/ml

Ni = 100 ug/ml, Co = 100 ug/ml, Cr = 6 ug/ml.

These solutions were analyzed several times and the standard

deviation of results was found to be ±7%.

(31 Sensitivity

Sensitivities were compared with those reported by

Dvorak (6) for single element determinations using a nitrous

oxide-acetylene flame. This comparison is shown in Table 1.

TABLE 1

Comparison of Sensitivities(ppm/1% Transmission!

Dvorak CRNL

Copper

Cobalt

Nickel

Iron

Chromium

0.6

3.4

1.6

2 .5

0.4

2 .0

1.2

1.1

0 . 1

DISCUSSION

The system developed has proven to give satisfactory

reproducibility and sensitivity for standard solutions of five

elements in a monitoring mode. The system is versatile enough

to do sequential batch analyses or continuous on-line monitoring.

The instrument should not be limited to flame emission but could

be used for atomic absorption (using multi -element lamp) or

fluorescence measurements.

Since a peak signal is obtained for a pre-selected time,

the signal lends itself to averaging for better results. l\e

are developing a data processing system based on a programmable

calculator to take advantage of this feature.

REFERENCES

1. B.L. Vallee and M. Margoshes, Anal. Chem. 2_8, 175 (1956)

2. J.V. Sullivan and A. Walsh, Spec. Chim. Acta. 2J_, No. 4, "27 C19bS)

3. J.B. Dawson, D.J. Ellis and R. Milner, Spec. Chim. Acta.

23-B, 695 (1968)

4. D.G. Mitchell, Technicon International Congress, Nov. 24,

1970, New York

5. H.V. Malmstead and E. Cordos, American Laboratory,

Aug. 1972, p. 35

6. J. Dvorak, "Flame Photometry - Laboratory Practice",

Butterworth § Company (Canada) Ltd., Toronto

8 -

7. J.A. Dean and T.C. Rains, "Flame Emission and Atomic

Absorption Spectrometry", Vol. 1, p. 390 (1969). Marcel

^ekker Ltd., New York

8. D.L. Cook et al. Lab. Practice 21, No. 3, 171

3551-G

FIGURE I

ELECTRICAL PLUGS

\

TERMINAL STRIPS

WAVE LENGTH SELECTOR

WAVE LENGTHSCANNER

TRACKING SWITCH SHOWN INENERGIZEDDE.ENERGIZED

POSITIONSTRIPPER

.ROTATION

END VIEW ON DRUM

^^'^^^*m^mmmm^£sff^^m ^X s ir"1 / - ' ** vj FIGURE 2 KRAMER ELECTRO-MEGHAN ICAL PROGRAMMER

• r- ."...• t

- L

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FIG. 3 ELECTRICAL CIRCUIT FOR CRAMER PROGRAMMER

b!_3S- S •« U M

o

o

i

S - .ass

F I G U R E 5 T Y P I C A L RECORDER READOUT

2 min.CYCL

2 min.CYCLE

Cr - 0 . 2 5 p p m I N AQUEOUS

- 2 . 5 p p m I N AQUEOUS

2 min.CYCLE

i.

N i - 2. 5 p p m I N A Q U E O U S

W A V E L E N G T H S E L E C T O R F U L L C Y C L E

2 m i n .CYCLE

- 2 . 5 p p m I N A Q U E O U S

2 m i n .CYCLE C u - 1 p p m I N A Q U E O U S

25sec|"NEW |qYCLE"

j_1

. .L.

5

Tlu International Standard Serial Number

ISSN 0067-0367

has been assigned to this series of reports.

To identify individual documents in the serieswe have assigned an AECL—number.

Please refer to the AECL-number whenrequesting additional copies of this document

from

Scientific Document Distribution OfficeAtomic Energy of Canada Limited

Chalk River, Ontario, Canada

KOJ I JO

Price S2.00 per copy

39-76