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Code: METH12V01

Date: July 27, 2014

Author: Robin Chacha

STANDARD OPERATING PROCEDURES

METHOD FOR ANALYSING SOIL, PLANT AND LIQUID SAMPLES FOR TOTAL ELEMENTS USING XRF ANALYSIS

Contact Details: Telephone: +254 (20) 7224000/4235/4279/4163 Email: [email protected] : Laboratory Manager, [email protected] Website: www. http://worldagroforestry.org/research/land-health

Address Details: World Agroforestry Centre, Mailing: P.O Box 30677-00100 Nairobi, Kenya Physical address: United Nations Avenue Off Limuru Road, Gigiri, Nairobi, Kenya

mailto:[email protected]

mailto:[email protected]

STANDARD OPERATING PROCEDURE Date: July 27, 2014

Code: METH12V01 Title: Method for analysing soil samples for total elemental using XRF analysis


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METHOD DOCUMENT CONTROL LOG

Name and position Signature

Author(s)

Hezekiah Nyandika - Laboratory Technician Robin Chacha - Senior Laboratory Technician

[signature for completeness and correctness of document]

Verifiers Robin Chacha - Senior Laboratory Technician



Authorizer Mercy Nyambura – Laboratory Manager [signature for completeness and correctness of document]

Distribution of valid copies of this document: G143C

Total X-Ray Fluorescence lab

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Historical data [dates of previous issues]

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SCOPE AND APPLICATION

This is a Standard Operating Procedure developed and validated by the World Agroforestry

Centre’s Soil-Plant Spectral Diagnostic Laboratory for total element analysis in soil, plant and

liquid samples using the Bruker S2 Picofox Total X-ray Fluorescence technique. The protocol

includes total element profiling in suspended milled solid material, soil-water extracts,

suspended and liquids. TXRF technique is a rather versatile and cost-effective method for multi-

elemental analysis. The spectrometer can be used for element trace analysis in various fields of

research for minute specimens, such as small grains or gels deposited in the sample carrier. Due

to the improvement in signal to noise ratio, the instrumental detection limits are typically in the

range of ppm or ppb. The data is acquired from a very thin layer of sample on a quartz sample

carrier discs and elemental quantification is made possible due to presence of internal standard

as well as the elemental atomic numbers. TXRF detects elements from Na (11) to U (92).

PRINCIPLE

Total X-ray fluorescence spectroscopy (TXRF) determines concentrations of major and trace

elements in multiple media. Total X-ray fluorescence (TXRF) method is used for routine,

relatively non-destructive elemental analyses of suspensions, solids, rocks, liquids and plant

materials. The technique is appropriate because it has a low cost of sample preparation;

stability and ease of use of x-ray spectrometers make this one of the most widely used methods

for analysis of major and trace elements. A TXRF spectrometer works because when an intense

X-ray beam, known as the incident beam, hits an inner shell electron in a sample atom; the

electron is removed leaving the atom in an excited state. An electron from an outer shell

replaces the missing inner shell electron. The energy difference between the inner and outer

shell is balanced by the emission of a photon quantum (fluorescence radiation). The energy,

and therefore the wavelength, of the x-ray fluorescence radiation is characteristic (finger print)

for the different elements. The intensity of the x-ray fluorescence radiation is, as a first




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approximation, proportional to element concentration. Quantification in total reflection x-ray

fluorescence spectroscopy is possible by, known concentration and net intensity of an internal

standard element, net intensity of element lines, sensitivity of the instrument for element lines

(energy-dependent).

ABBREVIATIONS AND DEFINITIONS

TXRF - Total X-ray Fluorescence

LLD - Lower Limit Detection

Na - Sodium

U - Uranium

RELATED DOCUMENT

HS 07 Safety Manual

TXRF Laboratory Logbook

Soil sample preparation and handling

Plant sample preparation and handling

Water sample preparation and handling

Protocol for updating, backup and management of database

METH 12 (Method for analysing soil, plant and liquid samples for total elements using

XRF analysis)

EQUP07 (XRF)

EQUP17 (McCrone Micronizing Mill)




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RELATED FORMS

WF 11- Soil Multi-element Analysis using a Bruker S2 Picofox Total X-ray Fluorescence

Spectrometer workflow

Sample weight record sheet

SAFETY AND ENVIRONMENT

When procured, Bruker AXS Microanalysis GmbH has taken all measures and provided technical

precautions to protect the users against danger by X-ray radiation, electrical current and

injuries. This requires the user’s thoroughly attention and compliance with all safety

instructions. All possible constructive measures have been implemented to avoid X-ray

radiation hazards for the personnel. The manufacturer must have familiarized at least one

person of the operating staff with the technical and safe application. Total X-ray fluorescence

spectrometers comply with national regulations relevant to radiation protection from

international authenticating institutions. The operating technician involved in X-ray

fluorescence analysis shall qualify for managing or supervising the operation of X-ray apparatus

according to national regulations. The S2 PICOFOX must just be operated with functional safety

equipment. Observing the safety rules can prevent a risk of X-ray radiation for the operator due

to the measures taken and the technical installations provided by the manufacturer.

For all other safety awareness and precautionary inform refer to the X-ray laboratory safety

manual and Material Safety Data Sheet for a complete warning. (Refer to the appropriate SOP if

applicable)




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REQUIREMENTS

Equipment:

a. Horizontal Laminar Airflow Cabinet HLF12 outflow .41m/s

b. Laboratory fume extract hood

c. S2 Picofox, Bruker TXRF spectrometer

d. Oven, Memmert, model UNE 400 temperature 300C to 2500C

e. Sonic water bath VWR Ultra, 42KHz Sonics

f. Micronizing mill Glen Creston McCrone

g. IKA MS 3 Vortex mixer, variable speed max 3000rpm

h. Hot plate, Stuart SD 300 temperature controlled max 3000C

i. Magnetic stirrer, Stuart SB 161

j. Micro balance 0.0001 g readability, Mettler AB104-S, min wt. 10mg,max 110g

k. Computer with S2 Picofox and R script and File maker software

l. Water purification system Elga CENTRA

m. Centrifuge Eppendorf 5810

Materials & Supplies

a. Volumetric pipettes (1 – 10 ml, 500 – 5000 µl, 25 – 250 µl, 0.5 – 10 µl)

b. Pyrex beaker (1000 ml, 800ml, 50ml)

c. Micro spatula

d. Volumetric flasks (1000ml, 500 ml, 250ml, 100ml)

e. Sample vials racks

f. PTFE beakers (400ml)

g. Washing cassette 25 positions Sample carrier cassette 25 positions

h. Quartz glass sample carrier 30 mm x 3 mm

i. Sample centering auxiliary tool

j. Storage container for pure water (10 L)

k. Wash bottles




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l. Watch glass

m. Q tip

n. Cleaning tissues (fluff-free)

o. Clear 5 ml capacity sample vials

p. Pipette tips (various)

q. Safety gloves (powder and talcum free)

Chemicals

a. Nitric acid, minimum P.A 10 % (GPR grade)

b. Alkaline cleaning solution (Teepol, 5% RBS 50TM or Decon 90)

c. Acetone, (reagent grade)

d. Silicon solution in isopropanol

e. Triton X-100 standard grade

f. Mono-element standards (normal ICP mono-element standards, which come with a

concentration of 1 g/l and a low nitric acid matrix

g. Arsenic standard 1000 ppm ICP grade

h. Gallium standard 1000 mg/l, ICP grade

i. Selenium standard 1000mg/l, ICP grade

j. Scandium standard 1000mg/l, ICP grade

k. Yttrium standard 1000 mg/l, ICP grade

l. Merck multi-element standard 100 mg/l ICP grade

m. Kraft Multi-element standard 10 mg/l Ca,As,Cu,Mn, Mg

Reagents

a. Prepare 1% Triton X-100 solution by transferring 1ml of Triton X-100 to a labeled 100

ml volumetric flask. Make up to volume using pure water.

b. Prepare 10 % Cleaning solution by transferring 500ml of RBS cleaning solution into a

5000ml volumetric flask. Mix well and make to volume using pure water.




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c. Prepare 10% Nitric acid by adding 300ml of pure water into a 500ml volumetric flask

and while stirring add 50ml of concentrated Nitric acid carefully into the flask. Mix

well and make to volume using pure water.

d. Silicon solution in isopropanol e.g. Serva

PROCEDURE

Sample processing and preparation

a. Soils are dried and sieved through 2-mm sieve. Soil sample (45mg) is weighed into a

5ml centrifuge tube and 2.5ml of an aqueous Triton X100 solution is added. 40 µl of

1000 mg/l Se internal standard solution is added into the suspension using a

calibrated pipette. Suspension is mixed thoroughly and sonicated. 10µl of

suspension is transferred onto a siliconized quartz disc and dried.

b. Plants are dried and milled to pass through a 1-mm sieve. Plant sample (45mg) is

weighed into a 5ml centrifuge tube and 2.5ml of an aqueous Triton X100 solution is

added. 40 µl of 1000 mg/l Sc internal standard solution and 10 µl of 1000 mg/l Y are

added into the suspension using calibrated pipettes. Suspension is mixed thoroughly

and sonicated. 10µl of suspension is transferred onto a siliconized quartz disc and

dried.

c. Liquid samples are a diluted appropriately. Different dilutions can be tested to find

an optimal peak to scattering background ratio. Liquid specimen (1000 µl) is sampled

into a labeled vial. For accurate determination of light elements only, 40 µl of 100

mg/l Sc single element standard into the liquid sample. For determination of heavier

elements, in addition transfer10 µl of 100 mg/l Y single element internal standard

using a calibrated pipette into the liquid sample. Note the 10 times dilution of the

standards compared with the soil and plant methods.




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Measurement (Refer to operator manual)

a. Take the TXRF spectrometer and control computer to operation and measurement

mode. Switch on the X-ray tube

b. Carefully place the samples in the Quartz glass sample carrier 30 mm x 3 mm into

the auto sampler compartment spectrometer.

c. Open the measurement software and prepare a measurement job by filling in

sample details and save the measurement job. Solid, plants, suspension and liquid

sample all have different operating variables. Refer to measurement SOP.

d. Perform reference drive of the sample changer and start data acquisition by

selecting ‘Start’.

e. The ICRAF methods allow automatic processing of gain correction, multi-element

measurement and the evaluation of spectra after the end of the measurement. All

completed measurements and spectra are saved in the project file. Refer to Annex 2

for quantification methods.

f. Spectra software acquires qualitative raw spectra and quantifies the elemental

results and stores the project files within the software upon completion of

measurement job. The results are exported to collecting PC in .csv file format and

only elemental, Lower detectable limit and Sigma value are extracted for data

analysis and reporting using R-software program.

QUALITY CONTROL

A quality management system is used in the laboratory as the basis for a constantly high quality

of analytical services. It involves the monitoring of the most important analytical features of the

S2 spectrometer and the methodology.

Quality of results obtained using TXRF technique greatly impacted by the accuracy of the

instrument sensitivity curve. The sensitivity is determined by the measurement of a 1-ng-Ni

sample and states, which fluorescence intensity standardized on mass, time and tube current is

detected by the present instrument.




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Comparative measurements with other reference multi element standards are also used to test

the sensitivity. The results of the standards used are used to decide whether recalibration if

necessary.

The gain correction is performed daily for the fine adjustments of spectronic amplification using

a mono element standard. It does not just include the inspection of an instrument parameter

but simultaneously indicate abnormal deviations from the nominal value.

Spectronic resolution test is done monthly. The spectroscopic resolution has a significant

influence on the analytical performance of the instrument. A permanent deterioration of the

resolution can be an indication of a defect inside the detector or in the signal amplifier.

Multi-element standards are used for the testing of quantification accuracy and reproducibility

of results. Upon the spectra evaluation, a report is generated and the nominal values are

compared to the measurement data.

Research samples are measured in triplicates to assess repeatability.

REFERENCES

S2 Picofoxtm User manual, Bruker advanced x-ray solutions

Pre-installation manual

Test log of the protective earthing conductor

Data sheet X-ray tube

CE-conformity declaration

Safety data sheet Beryllium according to the EU directive 91/155/EWG




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ANNEX 1. Workflow

Soil & Plant Sample

Milling to <53 µm

Weighing 45mg

Internal Standard and reagent addition

Sonication

Pipetting

Centrifugation

Soil-water

suspension

Liquid sample

Standard Addition

10% Cleaning solution

10% Nitric acid treatment

Hot water treatment

Oven drying at 80oC

Siliconizing

Drying (hot plate at 50oC)

XRF sample measurement

GO TO DATABASE

Mechanical WipingAcetone

RinsingType 1 water

Acetone wiping

HHXRF Sample CupAssembly

Loading

HHXRFMeasurement

Data FilteringR & Knime

Supernatant

Data Acquisition

Quartz disc cleaning

Pipetting

Standard Addition

Action Point

Terminal Point

Process route

LEGEND

RinsingType 1 water

RinsingType 1 water

Soil & Plant Sample

Milling to <53 µm

Liquid sample

Sample type?

Sample from processing factory

Total X-Ray Flourescence Laboratory

Workflow

Objective:

To achieve an economical detailed rapid screening analysis of

elemental composition of liquid and solid samples




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ANNEX 2: STANDARD REFERENCE FACT SHEET

Reference standard Origin Calibration Frequency

Arsenic mono-element standard

Bruker Gain correction - Fine adjustment of spectronic amplification.

Each run, daily

1 ng Nickel standard Bruker Instrument sensitivity and detection limit

Monthly

1g/l Manganese standard Bruker Spectroscopic resolution - FWHM

Monthly

Merck multi-element standard 100mg/l conc

Bruker Accuracy of quantification Weekly

Kraft multi-element standard 10 mg/l conc

Bruker Accuracy of quantification Weekly

INTERNAL STANDARDS Selenium, ICP 1000 ppm in 2% HNO3

Commercial standard Internal standard- soil Every run, daily

Yttrium, ICP 1000 ppm in 2% HNO3

Commercial standard Internal standard - plants Every run, daily

Gallium, ICP 1000 ppm in 2% HNO3

Commercial standard Internal standard - liquid Every run, daily

Scandium, ICP 1000 ppm in 2% HNO3

Commercial standard Internal standard - plants Every run, daily

1% Triton X-100 Commercial Blank – Liquid and soil water

Every run, daily

SOIL REFERENCE MATERIAL Katumani soil KARI, Machakos Internal standard Every batch of 32 soil

samples B1519_2649 soil Embu ,Kenya Soil method calibration B1519_2773 soil Embu ,Kenya Soil method calibration B2222_6534 soil Funyula Busia, Kenya Soil method calibration B2222_6560 soil Funyula Busia, Kenya Soil method calibration B765_8139 soil Western Kenya Soil method calibration B765_8430 soil Western Kenya Soil method calibration B765_8721 soil Western Kenya Soil method calibration B793_100 soil Western Kenya Soil method calibration B793_289 soil Western Kenya Soil method calibration B793_86 soil Western Kenya Soil method calibration FS18_7909 soil Madagascar Soil method calibration FS18_8064 soil Madagascar Soil method calibration FS18_8269 soil Madagascar Soil method calibration FS18_8269 soil Madagascar Soil method calibration

PLANT REFERENCE MATERIAL Apple mango Local, Kenya Plant method

development & calibration

Brown cowpeas

Local, Kenya Plant method




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development & calibration Cowpeas leaves Local, Kenya Plant method

development & calibration

Croton leaves Local, Kenya Plant method development & calibration

Cyprus Bark Local, Kenya Plant method development & calibration

Kent mangoes Local, Kenya Plant method development & calibration

Mahogany_ Local, Kenya Plant method development & calibration

Maize leaves Local, Kenya Plant method development & calibration

Mango leaves Local, Kenya Plant method development & calibration

NIST_1515 Commercial std , NIST Plant method development & calibration

NIST_1515a Commercial std , NIST Plant method development & calibration





Prunus bark Local, Kenya Plant method development & calibration

Prunus Leaves Local, Kenya Plant method development & calibration

White cowpeas Local, Kenya Plant method development & calibration

Apple Mangoes Local, Kenya Plant method development & calibration

Brown Cowpeas Local, Kenya Plant method development & calibration

Mango leaves Nairobi, Kenya Plant method development & calibration

Wheat flour Nairobi, Kenya Plant method development & calibration

Bamboo leaves ICRAF, Nairobi Plant method development & calibration

Mango pulp Machakos, Kenya Plant method development & calibration

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