Soil quality — Determination of elemental composition by X-ray fluorescence

ISO 18227:2014 specifies the procedure for a quantitative determination of major and trace element concentrations in homogeneous solid waste, soil, and soil-like material by energy dispersive X-ray fluorescence (EDXRF) spectrometry or wavelength dispersive X-ray fluorescence (WDXRF) spectrometry using a calibration with matrix-matched standards. ISO 18227:2014 is applicable for the following elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, I, Cs, Ba, Ta, W, Hg, Tl, Pb, Bi, Th, and U. Concentration levels between approximately 0,000 1 % and 100 % can be determined depending on the element and the instrument used.

Qualité du sol — Détermination de la composition élémentaire par fluorescence X

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Status
Published
Publication Date
18-Feb-2014
Current Stage
9092 - International Standard to be revised
Start Date
09-Jul-2021
Completion Date
24-Oct-2022
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INTERNATIONAL ISO
STANDARD 18227
First edition
2014-03-01
Soil quality — Determination of
elemental composition by X-ray
fluorescence
Qualité du sol — Détermination de la composition élémentaire par
fluorescence X
Reference number
ISO 18227:2014(E)
ISO 2014
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ISO 18227:2014(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2014

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Published in Switzerland
ii © ISO 2014 – All rights reserved
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ISO 18227:2014(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Safety remarks ........................................................................................................................................................................................................ 3

5 Principle ........................................................................................................................................................................................................................ 3

6 Apparatus ..................................................................................................................................................................................................................... 3

7 Reagents ........................................................................................................................................................................................................................ 4

8 Interferences and sources of error .................................................................................................................................................... 5

9 Sample preparation ........................................................................................................................................................................................... 5

9.1 General ........................................................................................................................................................................................................... 5

9.2 Drying and determination of dry mass .............................................................................................................................. 6

9.3 Preparation of pressed pellet ..................................................................................................................................................... 6

9.4 Preparation of fused beads ........................................................................................................................................................... 6

10 Procedure..................................................................................................................................................................................................................... 7

10.1 Analytical measurement conditions ..................................................................................................................................... 7

10.2 Calibration .................................................................................................................................................................................................. 8

11 Quality control .....................................................................................................................................................................................................13

11.1 Drift correction procedure .........................................................................................................................................................13

11.2 Blank test ..................................................................................................................................................................................................14

11.3 Reference materials .........................................................................................................................................................................14

12 Calculation of the result .............................................................................................................................................................................14

13 Test report ................................................................................................................................................................................................................14

Annex A (informative) Semi-quantitative screening analysis of waste, sludge, and soil samples .....15

Annex B (informative) Examples for operational steps of the sample preparation for soil and

waste samples ......................................................................................................................................................................................................18

Annex C (informative) Suggested analytical lines, crystals, and operating conditions ................................23

Annex D (informative) List of reference materials applicable for XRF analysis ..................................................26

Annex E (informative) Validation ..........................................................................................................................................................................28

Bibliography .............................................................................................................................................................................................................................37

© ISO 2014 – All rights reserved iii
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ISO 18227:2014(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers

to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 190, Soil quality, Subcommittee SC 3, Chemical

methods and soil characteristics.
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ISO 18227:2014(E)
Introduction

X-ray fluorescence spectrometry is a fast and reliable method for the quantitative analysis of the total

content of certain elements within different matrices.

The quality of the results obtained depends very closely on the type of instrument used, e.g. bench top or

high performance, energy dispersive or wavelength dispersive instruments. When selecting a specific

instrument, several factors have to be considered, such as the matrices to be analysed, the elements

to be determined, the detection limits required, and the measuring times. The quality of the results

depends on the element to be determined and on the surrounding matrix.

Due to the wide range of matrix compositions and the lack of suitable reference materials in the case

of inhomogeneous matrices such as waste, it is generally difficult to set up a calibration with matrix-

matched reference materials.
Therefore, this International Standard describes two different procedures:

— a quantitative analytical procedure for homogeneous solid waste, soil, and soil-like material in the

normative part. The calibration is based on matrix-matched standards;

— an XRF screening method for solid and liquid materials as waste, sludge, and soil in Annex A which

provides a total element characterization at a semi-quantitative level. The calibration is based on

matrix-independent calibration curves, previously set up by the manufacturer.

The technical content of this International Standard is identical with the European Standard

EN 15309:2007.
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INTERNATIONAL STANDARD ISO 18227:2014(E)
Soil quality — Determination of elemental composition by
X-ray fluorescence
1 Scope

This International Standard specifies the procedure for a quantitative determination of major and trace

element concentrations in homogeneous solid waste, soil, and soil-like material by energy dispersive

X-ray fluorescence (EDXRF) spectrometry or wavelength dispersive X-ray fluorescence (WDXRF)

spectrometry using a calibration with matrix-matched standards.

This International Standard is applicable for the following elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr,

Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, Te, I, Cs, Ba, Ta, W, Hg, Tl, Pb, Bi, Th,

and U. Concentration levels between approximately 0,000 1 % and 100 % can be determined depending

on the element and the instrument used.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

ISO 11464, Soil quality — Pretreatment of samples for physico-chemical analysis

ISO 11465, Soil quality — Determination of dry matter and water content on a mass basis — Gravimetric

method

ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories

EN 14346:2006, Characterization of waste — Calculation of dry matter by determination of dry residue or

water content

EN 15002:2006, Characterization of waste — Preparation of test portions from the laboratory sample

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE See References [11] and [14] for non-specified terms.
3.1
absorption edge
jump of the mass absorption coefficient at a specific wavelength or energy
3.2
absorption of X-rays

loss of intensity of X-rays by an isotropic and homogenous material as described by the Bouger-Lambert

law
3.3
analytical line

specific characteristic X-ray spectral line of the atom or ion of the analyte used for the determination of

the analyte content
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ISO 18227:2014(E)
3.4
continuous radiation

electromagnetic radiation produced by the acceleration of a charged particle, such as an electron, when

deflected by another charged particle, such as an atomic nucleus
3.5
Compton-line

spectral line due to incoherent scattering (Compton-effect) occurring when the incident X-ray photon

strike an atom without promoting fluorescence

Note 1 to entry: Energy is lost in the collision and therefore the resulting scattered X-ray photon is of lower energy

than the incident X-ray photon.
3.6
drift correction monitor
physically stable sample used to correct for instrumental drift
3.7
emitted sample X-ray

radiation emitted by a sample consisting of X-ray fluorescence radiation and scattered primary X-rays

3.8
fused bead
analyte sample prepared by dissolution in a flux
3.9
liquid sample
analyte sample submitted as a solution for direct measurement in the sample cup
3.10
mass absorption coefficient

constant describing the fractional decrease in the intensity of a beam of X-radiation as it passes through

an absorbing medium
Note 1 to entry: This is expressed in cm /g.

Note 2 to entry: The mass absorption coefficient is a function of the wavelength of the absorbed radiation and the

atomic number of the absorbing element.
3.11
polarized excitation X-ray spectrometer

energy dispersive X-ray spectrometer where the excitation is performed by polarized radiation and the

emitted X-ray fluorescence radiation is detected along the direction of polarization

3.12
powder sample
analyte sample submitted as a powder for direct measurement in the sample cup
3.13
precision

closeness of agreement of results obtained by applying the method several times under prescribed

conditions
[SOURCE: ISO 5725-2:1994]
3.14
pressed pellet
analyte sample prepared by pressing milled material into a disk
3.15
primary X-ray
X-ray by which the sample is radiated
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ISO 18227:2014(E)
3.16
quality control sample

stable sample with known contents, e.g. certified reference material (CRM), used to monitor instrument

and calibration performance
3.17
X-ray fluorescence radiation

emission of characteristic X-rays from a sample that has been bombarded by high-energy X-rays or

gamma rays
4 Safety remarks

Anyone dealing with waste and sludge analysis has to be aware of the typical risks that this kind of

material presents irrespective of the parameter to be determined. Waste and sludge samples can

contain hazardous e.g. toxic, reactive, flammable, and infectious substances, which could potentially

undergo biological and/or chemical reaction. Consequently, it is recommended that these samples

should be handled with special care. The gases that can be produced by microbiological or chemical

activity are potentially flammable and pressurize sealed bottles. Bursting bottles are likely to result in

hazardous shrapnel, dust, and/or aerosol. National regulations should be followed with respect to all

hazards associated with this method.

The X-ray fluorescence spectrometer shall comply with international and national regulations relevant

to radiation protection.

The person responsible for managing or supervising the operation of X-ray equipment shall provide

evidence of his knowledge of radiation protection according to national regulations.

5 Principle

After a suitable preparation, if necessary, the sample is introduced into an XRF spectrometer and excited

by primary X-rays. The intensities of the secondary fluorescent energy lines specific for each element

are measured and the elemental composition of the sample is determined by reference to previously

established calibration graphs or equations and applying corrections for inter-element effects. The

calibration equations and inter-element corrections are established using pure reagents and/or series

of internal or reference materials providing they meet all the requirements of the relevant preparation

technique.
6 Apparatus

6.1 X-ray fluorescence spectrometer, shall be able to analyse the elements according to the scope of

this International Standard.
The following types of X-ray fluorescence spectrometers are applicable:

— energy dispersive X-ray fluorescence (EDXRF) spectrometer that achieves the dispersion of the

emitted X-ray fluorescence radiation by an energy dispersive detector;

— wavelength dispersive X-ray fluorescence (WDXRF) spectrometer that achieves the dispersion of

the emitted X-ray fluorescence radiation by diffraction by a crystal or a synthetic multilayer.

The spectrometer consists of a number of components:
— primary X-ray source, an X-ray tube with a high-voltage generator;
— a sample holder;
— detector unit including electronic equipment;
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ISO 18227:2014(E)

— source modifiers to modify the shape or intensity of the source spectrum or the beam shape (such

as source filters, secondary targets, polarizing targets, collimators, focusing optics, etc.).

The detector unit is different for WDXRF and for EDXRF spectrometers. WDXRF spectrometers take

advantage of the dispersion of the emitted radiation by scattering by a crystal or a synthetic multilayer.

The detector does not need to be capable of energy discrimination. EDXRF spectrometers use an

energy dispersive detector. Pulses of current from the detector, which are a measure of the energy of

the incoming X-rays, are segregated into channels according to energy using a multi-channel analyser

(MCA).

NOTE 1 The use of a high-energy X-ray tube increases the potential for losses of volatile analytes from samples

by heating in the spectrometer during analysis.

NOTE 2 The new generation of EDXRF spectrometers takes advantage of the polarizing target theory resulting

in a significant decrease of the background scattering, and therefore lower limits of detection can be achieved

(comparable to WDXRF).
6.2 Mill, preferable with walls made of agate, corundum, or zircon.

6.3 Pellet preparation equipment, manual or automatic pellet press, capable of providing a pressure

of at least 100 kN.
6.4 Aluminium cup, supporting backing cup for pressed pellets.

6.5 Fusion apparatus, electric, gas, or high-frequency induction furnace that can be heated up to a

fixed temperature of between 1 050 °C and 1 250 °C.

6.6 Fusion crucibles, crucibles made of non-wetting platinum alloy (Pt 95 %; Au 5 % is suitable).

Lids, if used, shall be made from platinum alloy.

NOTE Certain metal sulphides (so called platinum poisons) affect the platinum crucibles in which the sample

is melted.
6.7 Casting moulds, non-wetting platinum alloy (Pt 95 %; Au 5 % is suitable).
7 Reagents
The reagents mentioned are used as carrier material.
7.1 Binder, liquid or solid binder free of analytes of interest.

Solid materials can contain a certain amount of moisture, which shall be compensated for.

NOTE Different type of binders can be used. A binder commonly used is wax.
7.2 Flux, solid flux free of analytes of interest.

Solid materials can contain a certain amount of moisture, which shall be compensated for (see ISO 12677

for compensation for moisture in flux).

NOTE Different type of fluxes can be used. Fluxes commonly used are lithium metaborate, lithium tetraborate,

or mixtures of both.
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ISO 18227:2014(E)
8 Interferences and sources of error

The container in which the sample is delivered and stored can be a source of error. Its material shall be

chosen according to the elements to be determined.

NOTE Elemental Hg can penetrate polyethylene walls very rapidly in both directions. In the case of glass

containers, contamination can be observed for some elements, e.g. Al, As, Ba, Ce, K, Na, and Pb.

Interferences in X-ray fluorescence spectrometry are due to spectral line overlaps, matrix effects,

spectral artefacts, and particle size or mineralogical effects.

Spectral line overlaps occur when an analytical line cannot be resolved from the line of a different

element. Corrections for these interferences are made using the algorithms provided with the software.

Matrix effects occur when the X-ray fluorescence radiation from the analyte element is absorbed or

enhanced by other elements in the sample before it reaches the detector. In the case of complex matrices,

these effects generally have to be corrected.

Spectral artefacts, e.g. escape peaks, sum peaks, pulse pile up lines, dead time, and Bremsstrahlung

correction, are accounted for by the provided software. Spectral artefacts differ for energy dispersive

and wavelength dispersive XRF spectrometry.

Particle size effects can be reduced by milling the sample, and both particle size and mineralogical

effects can be eliminated by preparing bead samples. It is vital for quantitative analysis that the same

sample preparation procedure is applied to both the standards and the samples to be analysed.

9 Sample preparation
9.1 General

In analysis by XRF spectrometry, the sample preparation step is crucial as the quality of the sample

preparation strongly influences the accuracy of the results.

For quantitative analysis of solid samples, pressed pellets or fused beads have to be prepared. The

application of the pressed pellet method is recommended for the quantification of trace elements and

mandatory for the quantification of volatile elements, and the fused bead method for the determination

of non-volatile major and minor elements.

NOTE 1 The preparation of fused beads eliminates effects due to particle size and mineralogy.

The conditions of the preparation of fused beads shall be adapted to the matrix properties. Otherwise,

the preparation of fused beads can be difficult or can cause problems in case of waste-like matrices such

as sludges.

For a given calibration, the same preparation method shall be used throughout, for both samples and

standards.

NOTE 2 Depending on the sample type, other sample preparation methods can be applied according to Annex B.

For precise quantitative measurements, homogeneous and representative test portions are necessary.

Pre-treatment and preparation of test portions shall be carried out according to the appropriate clauses

of ISO 11464 and EN 15002. The particle size of the sample can strongly affect the precision of the

measurement. The particle size should preferably be smaller than 150 µm.

NOTE 3 Particle size smaller than 80 µm is recommended for the analysis of low atomic mass elements when

using the pressed pellet method.
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ISO 18227:2014(E)
9.2 Drying and determination of dry mass

Prepare and dry the sample according to ISO 11464 or EN 15002. Determine the dry mass according to

ISO 11465 or prEN 14346.
9.3 Preparation of pressed pellet

After drying and milling or grinding the sample, a pellet is prepared in the pellet press (6.3). Before

pressing, the sample shall be mixed and homogenized with a binder (7.1) in a ratio of sample:binder of

10:1 by weight. For the preparation of 40 mm in diameter pellets, about 10,0 g of sample is taken; for

32 mm in diameter pellets, about 4,5 g of sample is required. The amount of binder in the pellet shall be

taken into account for the dilution factor. It is recommended to press the sample in an aluminium cup

(6.4) as support.

NOTE 1 Different types of binders can be used. A binder commonly used is wax. In the case of a liquid binder,

the pellet is placed in an oven to evaporate organic solvent.
NOTE 2 Different dilution factors can be used.
9.4 Preparation of fused beads

After drying and milling or grinding the sample, a fused bead is prepared using the fusion apparatus

(6.5).

Ignite the sample at 1 025 °C ± 25 °C until constant mass is reached. Determine the loss on ignition at the

chosen temperature to correct for volatile elements and/or compounds being released during ignition

of the sample.
NOTE 1 The ignition temperature can vary depending on the sample matrix.

Because of the wide applicability of the fused bead technique, various fluxes and modes of calibration are

permitted providing they have been demonstrated to be able to meet certain criteria of reproducibility,

sensitivity, and accuracy.

For application of alkaline fusion technique (e.g. selection of flux, fusion temperature, and additives),

ISO 14869-2 or CEN/TR 15018 should be used.

NOTE 2 Fluxes commonly used are lithium metaborate, lithium tetraborate, or mixtures of both.

NOTE 3 Loss of volatile elements, e.g. As, Br, Cd, Cl, Hg, I, S, Sb, Se, and Tl, can occur during the fusion process.

Also, Cu can be volatile if a bromide-releasing agent is used.

The flux (7.2) is added to the ignited material in a dilution ratio of sample:flux of 1:5 by weight. For the

preparation of 40 mm in diameter beads, about 1,6 g of ignited sample is taken; for 32 mm in diameter

beads, about 0,8 g of ignited sample is required. The amount of flux in the bead shall be taken into account

for the dilution factor. The same sample preparation procedure and ratio of sample to flux shall be used

for samples and standards. The beads produced should be visually homogeneous and transparent.

NOTE 4 Non-ignited material can be used to prepare beads but, nevertheless, loss of ignition needs to be

determined and needs to be taken into account in the calculation of the results. It should be noted that non-ignited

material can contain compounds that can damage the platinum crucibles during fusion.

NOTE 5 Different dilution factors can be used.

After fusion in a platinum-gold crucible (6.6) the melt is poured into a casting mould (6.7) to make a

bead.

Beads can deteriorate because of adverse temperature and humidity conditions, so it is recommended

that beads are stored in desiccators.
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ISO 18227:2014(E)
10 Procedure
10.1 Analytical measurement conditions
10.1.1 Wavelength dispersive instruments

The analytical lines to be used and the suggested operating conditions are given in Table C.1. The

settings are strongly dependent on the spectrometer configuration, e.g. the type of X-ray tube (Rh, Cr),

tube power, available crystals, and type of collimators.
10.1.1.1 Intensities and background corrections

For the determination of trace elements, the measured intensities have to be background-corrected.

The measured background positions should be free of spectral line interferences. The net peak intensity

I, expressed as the number of counts per second of the element of interest, is calculated as the difference

between the measured peak intensity of the element and the background intensity:
II=−I (1)
where

is the count rate of the element i, expressed as the number of counts per second;

is the background count rate of the element i, expressed as the number of counts per second.

10.1.1.2 Counting time

The minimum counting time is the time necessary to achieve an uncertainty (2σ ), which is less than

the desired precision of the measurement. Choose a reference material with a concentration level in the

middle of the working range and measure the count rate. The counting time for each element can be

calculated according to Formula (2):
 
100 1
 
t = . (2)
 
II−
 
where
t is the total counting time for the peaks and background, in seconds;

is the relative target precision at a confidence level of 95 %, expressed as percentage.

10.1.2 Energy dispersive instruments

The analytical lines to be used and the suggested operating conditions are given in Table C.2. The

settings are strongly dependent on the spectrometer configuration, e.g. type of X-ray tube (Rh, Pd), tube

power, available targets, and type of filters.
Intensities and background corrections

Deconvolution of the spectra and background correction are needed when analysing the samples with

overlapping lines. Usually, XRF instruments are supplied with a specific software module for that

purpose.
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ISO 18227:2014(E)
10.2 Calibration
10.2.1 General

The calibration procedure is similar for energy dispersive and wavelength dispersive techniques.

In general, calibration is established by using matrix-adapted reference materials. The calibration

equations and inter-element corr
...

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