EN ISO 22940:2021

SLOVENSKI STANDARD
01-november-2021
Trdna alternativna goriva - Določevanje elementne sestave z rentgensko
fluorescenco (ISO 22940:2021)
Solid recovered fuels - Determination of elemental composition by X-ray fluorescence
(ISO 22940:2021)
Feste Sekundärbrennstoffe - Bestimmung der Elementzusammensetzung durch
Röntgenfluoreszenz (ISO 22940:2021)
Combustibles solides de recupération - Détermination de la composition élémentaire par
fluorescence de rayons X (ISO 22940:2021)
Ta slovenski standard je istoveten z: EN ISO 22940:2021
ICS:
75.160.10 Trda goriva Solid fuels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 22940
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2021
EUROPÄISCHE NORM
ICS 75.160.10
English Version
Solid recovered fuels - Determination of elemental
composition by X-ray fluorescence (ISO 22940:2021)
Combustibles solides de recupération - Détermination Feste Sekundärbrennstoffe - Bestimmung der
de la composition élémentaire par fluorescence de Elementzusammensetzung durch Röntgenfluoreszenz
rayons X (ISO 22940:2021) (ISO 22940:2021)
This European Standard was approved by CEN on 16 August 2021.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 22940:2021 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 22940:2021) has been prepared by Technical Committee ISO/TC 300 "Solid
recovered materials, including solid recovered fuels" in collaboration with Technical Committee
CEN/TC 343 “Solid Recovered Fuels” the secretariat of which is held by SFS.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2022, and conflicting national standards shall
be withdrawn at the latest by March 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN websites.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 22940:2021 has been approved by CEN as EN ISO 22940:2021 without any modification.

INTERNATIONAL ISO
STANDARD 22940
First edition
2021-08
Solid recovered fuels — Determination
of elemental composition by X-ray
fluorescence
Combustibles solides de récupération — Détermination de la
composition élémentaire par fluorescence de rayons X
Reference number
ISO 22940:2021(E)
©
ISO 2021
ISO 22940:2021(E)
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
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CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
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Published in Switzerland
ii © ISO 2021 – All rights reserved

ISO 22940:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
4.1 Symbols . 3
4.2 Abbreviated terms . 4
5 Safety remarks . 4
6 Principle . 4
7 Apparatus . 4
8 Interferences and sources of error . 5
9 Sample preparation . 5
9.1 Preparation principles . 5
9.2 Drying of general analysis sample material . 5
9.3 Preparation of pressed pellet . 6
10 Procedure. 6
10.1 Analytical measurement conditions . 6
10.1.1 Wavelength-dispersive instruments . 6
10.1.2 Energy-dispersive instruments . 7
10.1.3 Intensities and background corrections . 7
10.2 Calibration . 8
10.2.1 General. 8
10.2.2 General calibration procedure . 8
10.2.3 Calibration procedure using the pressed pellet method (recommended method) 9
10.3 Procedures for correcting matrix effects .10
10.3.1 General.10
10.3.2 Internal standard correction using Compton (incoherent) scattering method .10
10.3.3 Fundamental parameter approach .10
10.3.4 Fundamental or theoretical influence coefficient method .10
10.3.5 Empirical alpha correction . .11
10.4 Analysis of the samples .11
11 Quality control .12
11.1 Drift correction procedure .12
11.2 Reference materials and quality control samples .12
12 Calculation of the result .12
13 Performance characteristics .13
14 Test report .13
Annex A (informative) Publicly available solid recovered fuel reference materials .14
Annex B (informative) Validation .15
Bibliography .38
ISO 22940:2021(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 of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 300, Solid recovered materials, including
solid recovered fuels, in collaboration with the European Committee for Standardization (CEN)
Technical Committee CEN/TC 343, Solid Recovered Fuels, in accordance with the Agreement on technical
cooperation between ISO and CEN (Vienna Agreement).
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved

ISO 22940:2021(E)
Introduction
X-ray fluorescence spectrometry can be used as a fast method for a qualitative overview of ash forming
elements and impurities. When calibration is based on reference materials or on matrix-matched
homogeneous solid recovered fuel samples with known content, X-ray fluorescence spectrometry can
be used for a quantitative analysis of the total content of the specified elements within different solid
recovered fuels.
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 need to be considered, such as the matrices to be analysed, elements
to be determined, detection limits required and the measuring time.
Due to the wide range of matrix compositions and the lack of suitable reference materials in the case
of solid recovered fuels from various origin, it is generally difficult to set up a calibration with matrix-
matched reference materials. Therefore, it is important to use several homogenized solid recovered fuel
samples with properties that sufficiently match the matrices of interest and whose content has been
derived by independent measurement techniques, for example total digestion of solid recovered fuels
and characterization of major and minor elements by measurement of digestion solutions with ICP-MS
or ICP-OES, or by other techniques such as elemental analysis using combustion technology on sulfur or
by combustion and ion chromatographic determination for chlorine.
This document describes two different procedures:
1) Quantitative analytical procedure for major elements of solid recovered fuels. The calibration is
based on different reference materials and solid recovered fuel samples with known content.
The elements described as major elements of solid recovered fuels are in fact major elements of the
fuel ashes more than of the fuels. The determination of these elements can be helpful to predict the
melting behaviour and slagging of the ashes. Moreover, contamination of fuel with sand or soil is
indicated by high values of several elements.
2) Total element characterization at a semiquantitative level for major and minor elements of solid
recovered fuels. The calibration is based on matrix-independent calibration curves, previously set
up by the manufacturer.
In general, the sensitivity of X-ray fluorescence is not sufficient for a determination of the content of
minor elements (trace metals) in solid recovered fuels. However, it is possible to use determination
of minor elements after calibration with solid recovered fuel samples with known content or at a
semiquantitative level based on matrix-independent calibration curves to collect data for higher
sample numbers, taking into account lower achievable precision. Therefore, it may be used to
reveal excessive contents of minor elements in solid recovered fuels.
INTERNATIONAL STANDARD ISO 22940:2021(E)
Solid recovered fuels — Determination of elemental
composition by X-ray fluorescence
1 Scope
This document specifies the procedure for a determination of major and minor element concentrations
in solid recovered fuel material by energy-dispersive X-ray fluorescence (EDXRF) spectrometry
or wavelength-dispersive X-ray fluorescence (WDXRF) spectrometry using a calibration with
solid recovered fuel reference materials or solid recovered fuel samples with known content. A
semiquantitative determination can be carried out using matrix independent standards.
This document is applicable to the following elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co,
Ni, Cu, Zn, As, Br, Mo, Cd, Sb, Sn, Tl and Pb. Concentration levels between approximately 0,000 1 % and
100 % can be determined depending on the element, the calibration materials used and the instrument
used.
NOTE X-ray fluorescence spectrometry can be used as a fast method for a qualitative overview of elements
and impurities and after suitable calibration it is very useful for determining major elements or even minor
elements (except Hg) in order to quickly identify increased concentrations of minor elements in solid recovered
fuels (SRF), for example during SRF-production.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 21637, Solid recovered fuels — Vocabulary
1)
ISO 21646, Solid recovered fuels — Sample preparation
ISO 21660-3, Solid recovered fuels — Determination of moisture content using the oven dry method —
Part 3: Moisture in general analysis sample
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21637 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
absorption edge
abrupt change in mass absorption coefficient at a specific wavelength or energy
3.2
absorption
loss of intensity of X-rays due to isotropic and homogenous material, as described by the Beer-Lambert
law
1) Under preparation. Stage at the time of publication: ISO/DIS 21646:2021.
ISO 22940:2021(E)
3.3
analytical line
specific characteristic X-ray spectral line of the atom or ion of the analyte used for determination of the
analyte content
3.4
continuous radiation (Bremsstrahlung)
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
strikes 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 monitors
physically stable samples used to correct for instrumental drift
3.7
emitted radiation
emitted sample X-rays
radiation emitted by sample consisting of X-ray fluorescence radiation (3.13) and scattered primary
X-rays (3.11)
3.8
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: It 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.
3.9
powder sample
analyte sample submitted as a powder for direct measurement in the sample cup
3.10
pressed pellet
analyte sample prepared by pressing milled material into a disk
3.11
primary X-rays
X-rays by which the sample is radiated
3.12
quality control sample
stable sample with known contents, for example (certified) reference material (CRM) or homogenized
solid recovered fuel samples from known origin whose contents have been derived by independent
analysis used to monitor instrument and calibration performance
3.13
X-ray fluorescence radiation
emission of characteristic X-rays from a sample that has been bombarded by high-energy X-rays or
gamma rays
2 © ISO 2021 – All rights reserved

ISO 22940:2021(E)
4 Symbols and abbreviated terms
4.1 Symbols
Al aluminium
As arsenic
Br bromine
Ca calcium
Cd cadmium
Cl chlorine
Co cobalt
Cr chromium
Cu copper
Fe iron
K potassium
Mg magnesium
Mn manganese
Mo molybdenum
Na sodium
Ni nickel
P phosphorus
Pb lead
S sulfur
Sb antimony
Si silicon
Sn tin
Ti titanium
Tl thallium
V vanadium
Zn zinc
ISO 22940:2021(E)
4.2 Abbreviated terms
EDXRF energy-dispersive x-ray fluorescence
MCA multi-channel analyser
WDXRF wavelength-dispersive x-ray fluorescence
5 Safety remarks
The organization shall be aware of applicable legal requirements relating to the X-ray fluorescence
spectrometer.
The person responsible for managing or supervising the operation of X-ray equipment shall provide
evidence of their knowledge of national regulations relating to radiation protection.
6 Principle
After a suitable preparation, 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, provided that they meet all the requirements of the relevant preparation
technique.
7 Apparatus
7.1 X-ray fluorescence spectrometer, which shall be able to analyse the elements according to the
scope of this document. The following types of X-ray fluorescence spectrometers are applicable:
— EDXRF spectrometer that achieves the dispersion of the emitted X-ray fluorescence radiation by an
energy-dispersive detector;
— 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 the following components:
— primary X-ray source, an X-ray tube with a high-voltage generator;
— sample holder;
— detector unit including electronic equipment;
— source modifiers to modify the shape or intensity of the source spectrum or the beam shape (e.g.
source filters, secondary targets, polarizing targets, collimators, focusing optics).
The detector unit is different for WDXRF and for EDXRF spectrometers. WDXRF spectrometers take
advantage of the dispersion of the emitted radiation by diffraction 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 an 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.
4 © ISO 2021 – All rights reserved

ISO 22940:2021(E)
NOTE 2 The new generation of EDXRF spectrometers takes advantage of the polarizing target theory. The
excitation is performed by polarized radiation. The emitted X-ray fluorescence radiation is detected along the
direction of polarization, resulting in a significant decrease of the background scattering, therefore lower limits
of detection can be achieved (comparable to WDXRF).
7.2 Pellet press, capable of providing a pressure of at least 30 kN. The pellet press may be a cold press
or a hot mould press, operating at temperatures not exceeding 180 °C.
8 Interferences and sources of error
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
instrument 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 shall be corrected. The correction procedure depends on the X-ray fluorescence
spectrometry system (EDXRF or WDXRF) and the apparatus type itself.
Spectral artefacts, for example escape peaks, sum peaks, pulse pile up lines, dead time and continuous
radiation (Bremsstrahlung) correction, are accounted for by the provided instrument software.
Spectral artefacts differ for energy-dispersive and wavelength-dispersive XRF spectrometry.
9 Sample preparation
9.1 Preparation principles
The sample preparation is very critical for XRF analysis of solid recovered fuels. The quality of sample
preparation strongly influences the accuracy of the results. The following different options exist:
— For quantitative analysis of solid recovered fuel samples, the preparation of pressed pellets from
prepared general analysis sample material is recommended.
— For semiquantitative analysis of solid recovered fuels, the general analysis material may be used
directly (in powder form); concerning samples of solid recovered fuel pellets, the original pellets may
be used directly without any sample preparation. It may be used to provide fast basic information
about the approximate composition of a sample. Similar results can be obtained using portable XRF
instruments for field analysis.
For a given calibration, the same preparation method shall be used throughout, for both samples and
standards.
For precise quantitative measurements, homogeneous and representative test portions are necessary.
The nominal top size of the material shall be 0,5 mm or less, following the procedure according to
ISO 21646.
9.2 Drying of general analysis sample material
Dry a sufficient amount of general analysis sample material in accordance with ISO 21660-3 immediately
before pressing pellets for XRF-analysis.
NOTE Concerning some XRF instruments, the applied vacuum will dry the general analysis sample material
during the determination, giving the same results as if the sample had been previously dried.
ISO 22940:2021(E)
9.3 Preparation of pressed pellet
A pellet is prepared in the pellet press (7.2). Before pressing, the sample shall be mixed and homogenized.
Use the same weight for any single set of standards and samples and add binder (e.g. wax or liquid
organic binder), if necessary.
For the preparation, follow the manufacturer’s instructions.
NOTE 1 Different binders can be used. In the case of organic liquid binders (approximately 0,6 % weight of
sample) the pressed pellet will be placed in an oven at between 70 °C and 100 °C for a minimum of 10 minutes
to evaporate the organic solvent or for the formation of long chain polymers formed by heating (e.g. PVP-
methylcellulose binders).
NOTE 2 In the case of wax binder, the ratio of the sample weight to wax is around 10:1.
10 Procedure
10.1 Analytical measurement conditions
10.1.1 Wavelength-dispersive instruments
10.1.1.1 General
The analytical lines to be used and suggested operating conditions are given in Table 1. The settings
strongly depend on the spectrometer configuration, e.g. the type of X-ray tube (Rh, Cr), tube power,
available crystals and type of collimators. The instrument manufacturer’s recommendations should be
followed in all cases.
10.1.1.2 Intensities and background corrections
For the determination of trace elements, the measured intensities shall 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 (i), is calculated as the
difference between the measured peak intensity of the element and the background intensity, as given
in Formula (1):
II=− I (1)
pb
where
I
is the count rate of the element i, expressed as the number of counts per second;
p
I
is the background count rate of the element i with no analyte present, expressed as the number
b
of counts per second.
10.1.1.3 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 or quality control sample 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):
TI=×10021σ − I (2)
()()
%p b
where
6 © ISO 2021 – All rights reserved

ISO 22940:2021(E)
T
is the total counting time for the peaks and background, expressed in seconds;
2σ
is the relative target precision at a confidence level of 95 %, expressed as a percentage.
%
10.1.2 Energy-dispersive instruments
The analytical lines to be used and suggested operating conditions are given in Table 1. The settings
strongly depend on the spectrometer configuration, e.g. type of X-ray tube (Rh, Pd), tube power,
available targets and types of filters. The instrument manufacturer’s recommendations should be
followed in all cases.
10.1.3 Intensities and background corrections
Deconvolution of the spectra and background correction are needed when analysing samples with
overlapping lines. Usually, XRF instruments are supplied with a specific software module for that
purpose.
Table 1 — Suggested analytical lines, spectral line overlaps and correction methods
Element Line Spectral line overlap Type of matrix correction method
Na Kα ZnLβ Alpha or FP
Mg Kα AsLα Alpha or FP
Al Kα BrLα Alpha or FP
Si Kα Alpha or FP
P Kα Alpha or FP
S Kα CoKα PbMα NbLβ Alpha or FP or MAC
Cl Kα Alpha or FP or MAC
K Kα Alpha or FP
Ca Kα Alpha or FP
Ti Kα BaLα ILβ Alpha or FP
V Kα Ti Kβ Alpha or FP or MAC
Cr Kα VKβ PbLα Alpha or FP or MAC
Mn Kα CrKβ Alpha or FP
Fe Kα MnKβ Alpha or FP
Co Kα FeKβ Alpha or FP or MAC
Ni Kα CoKβ Compton or FP or MAC
Cu Kα TaLα ThLβ Compton or FP or MAC
Zn Kα WLα Compton or FP or MAC
Kα PbLα
As Compton or FP or MAC
Kβ BrKα
Br Kα AsKβ Compton or FP or MAC
Mo Kα ZrKβ ULβ Compton or FP or MAC
Kα Compton or FP or MAC
Ag CrKβ
Lα Alpha or FP
Kα Compton or FP or MAC
Cd AgLβ
Lα Alpha or FP
Kα Compton or FP or MAC
Sb CoKβ
Lβ Alpha or FP or MAC
ISO 22940:2021(E)
Table 1 (continued)
Element Line Spectral line overlap Type of matrix correction method
Kα Compton or FP or MAC
Sn CoKα
Lβ Alpha or FP or MAC
Tl Lβ PbLβ Compton or FP or MAC
Pb Lβ ThLα BiLβ SnKα Compton or FP or MAC
NOTE See 10.2.1 for additional information on the type of matrix correction methods.
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-matched reference materials (if available) or
samples with known content of minor and major elements. The calibration equations and inter-element
corrections are calculated by the software of the instrument. An accuracy check is performed with
CRMs (if available for the matrix) or samples with known composition.
Different procedures for correcting matrix effects may be used according to the analytical accuracy
required.
— Scattered radiation method is based on the principle that the intensities of the analyte line and of
the Compton line are affected in the same proportion due to the overall mass absorption coefficient
of the sample. This linear relationship holds true when all analytes are at low concentrations (minor
elements) and their absorption coefficients are not affected by an adjacent absorption edge. In this
case, an internal Compton correction can be used. Besides that, a correction method using the
Compton intensity with mass absorption coefficients (MAC) is also applicable. In this method, the
intensities of the major elements are measured to apply a jump edge correction for the analysed
trace elements.
— Correction using the fundamental parameter approach (FP).
— Correction using theoretical correction coefficients (alphas), taking basic physical principles,
instrumental geometry and so on into account.
— Correction using empirical correction coefficients (alphas) based on regression analysis of standards
with known elemental concentrations. This procedure will normally need more standards than a
calibration based on theoretical correction coefficients.
10.2.2 General calibration procedure
The measurements of analyte lines of samples of known composition are needed for calibration
purposes. The basic formula implies a linear relationship between the intensity and the concentration,
as given in Formula (3):
Ca=+aI× (3)
ii,0 i,1i
where
8 © ISO 2021 – All rights reserved

ISO 22940:2021(E)
C
is the concentration of the element of interest, expressed as mg/kg or percentage dry matter;
i
a
is the intercept of the calibration curve;
i,0
a
is the slope of the calibration curve;
i,1
I
is the net intensity of the element of interest, expressed as counts per second.
i
Matrix effects shall be taken into account in X-ray spectrometry according to Formula (4):
Ca=+aI× ×M (4)
()
ii,0 i,1i
where M is the correction factor due to the matrix effects.
The matrix effect correction factor may consist of an internal standard Compton correction factor or
may be calculated from mathematical models.
10.2.3 Calibration procedure using the pressed pellet method (recommended method)
The pressed pellet method is used to determine the concentrations of major and minor elements.
Select calibration standards with a similar composition as the samples under investigation containing
the elements of interest and covering the concentration range of interest. The use of reference
materials from different recognized producers is recommended, if available for the matrix (see
Annex A). Otherwise, solid recovered fuel samples shall be used whose composition has been assessed
by independent analysis techniques (total contents of major and minor elements). The element
concentrations shall vary independently in the standards. If the calibration covers many elements in a
wide range of concentrations, a large number of calibration samples will possibly be necessary.
Prepare pressed pellets from the selected calibration standards according to 9.3.
Specify the analytical measurement method for EDXRF or WDXRF as described in 10.1.
Start up the XRF equipment according to the instrument manufacturer’s manual and measure the
calibration standards using the specified measurement method. All measurements shall be performed
under vacuum or inert atmosphere. A minimum of four different calibration samples with different
concentration should be used.
Follow the instructions in the instrument manufacturer’s manual to perform the regression, the
background correction, the line overlap correction and the matrix corrections for all elements
under consideration. In Table 1, the possible spectral line overlaps are indicated (dependent on the
configuration of the instrument) and also the matrix correction method that can be applied. For minor
elements with an absorption edge above the absorption edge of iron, a Compton internal standard
correction can be applied. Otherwise, a theoretical alpha correction or correction for the absorption
edge should be performed (for these corrections, all elements in the sample shall be analysed).
Depending on the type of instrument and the software programs available, alternative correction
methods can be applied. Validation of the final calibration curves shall demonstrate the measurement
uncertainty (=accuracy and precision) of the method.
Perform the regression calculation and verify that the correlation factors are within the limits required.
NOTE In the case of determination of minor elements it can be sufficient to take into account higher
measurement uncertainties.
ISO 22940:2021(E)
10.3 Procedures for correcting matrix effects
10.3.1 General
The use of correcting methods should be performed by users with a high level of expertise. The choice
for the different procedures should be taken in compliance with the manufacturer’s instructions.
10.3.2 Internal standard correction using Compton (incoherent) scattering method
The measured intensity of incoherent scattering may be used directly to compensate for matrix effects
or indirectly for the determination of the effective mass absorption coefficient, μ, to correct for matrix
effects. The compensation for matrix effects is based on a combination of sample preparation and
experimental intensity data but not on fundamental and experimental parameters.
The Compton scattering method can be expressed as Formula (5):
CC=×II× II (5)
() ()
i,ui,r inc,ri,r i,uinc,u
where
is the concentration of the element of interest i of the sample, expressed as mg/kg or percent-
C
i,u
age dry matter;
is the concentration of the element of interest i of the calibration reference material, expressed
C
i,r
as mg/kg or percentage dry matter;
I
is the intensity of the incoherent Compton line of the sample, expressed as counts per second;
inc,u
I
is the intensity of the incoherent Compton line element of the calibration reference material,
inc,r
expressed as counts per second;
is the intensity of the element of interest i of the sample, expressed as counts per second;
I
i,u
is the intensity of the element of interest i of the calibration reference material, expressed as
I
i,r
counts per second.
10.3.3 Fundamental parameter approach
The fundamental parameter approach uses the physical processes forming the basis of X-ray fluorescence
emission and scattering to construct a theoretical model for the correction of matrix effects in practice.
The correction term M is calculated from first principle expressions. These are derived from basic
X-ray physics and contain physical constants and parameters that include absorption and scattering
coefficients, fluorescence yield, primary spectral distributions and spectrometry geometry.
The use of scattered radiation (Compton, Rayleigh or both) allows the determination of matrix effects
caused by sample elements that cannot be measured directly. The calculation of analyte concentrations
in samples is based on making successively better estimates of composition by an iteration procedure.
These iteration cycles are performed until the difference between the compared results is below a
defined value.
NOTE The algorithm used for the procedure is usually implemented in the manufacturer’s software.
10.3.4 Fundamental or theoretical influence coefficient method
The fundamental influence coefficient method encompasses any mathematical expression relating
emitted intensities and concentrations in which the influence coefficients are defined and derived
explicitly in terms of fundamental parameters.
10 © ISO 2021 – All rights reserved

ISO 22940:2021(E)
The calculation of the concentration from the intensities is performed by linear regression whereby
the net intensities are corrected for the present matrix effects. For each element, the concentration is
calculated according to Formula (6) and Formula (7):
CC=× IC1+∑α ××IM (6)
()()()
i,ui,r i,rijjri,u
CC=× IC11+∑αα××IC+∑ (7)
()()() ()
i,ui,r i,rijjri,u ij ju
where
is the concentration of the element of interest i of the sample, expressed as mg/kg or percentage
C
i,u
dry matter;
is the concentration of the element of interest i of the calibration reference material, expressed
C
i,r
as mg/kg or percentage dry matter;
is the intensity of the element of interest
...