ISO 16666:2025

International
Standard
ISO 16666
First edition
Surface chemical analysis — Total
2025-11
reflection X-ray fluorescence
— Principles and general
requirements
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviations . 1
3.1 Abbreviated terms .1
4 Physical background of TXRF . 2
4.1 General .2
4.2 Definition of angle and X-ray path in TXRF geometry .3
4.3 Beam projection .4
4.4 X-ray standing waves (XSW) .4
4.5 Fluorescence intensity .6
5 Instrumental requirements . . 6
5.1 Description of various possible TXRF measurement setups .6
5.2 Beam conditioning .8
5.2.1 Requirement .8
5.2.2 Beam guidance .8
5.2.3 Beam modulation (tuning) .8
5.2.4 Measurement angles in TXRF .8
5.3 Reflector (sample carrier) .9
5.3.1 General requirements .9
5.3.2 Reflectors for chemical analysis.9
5.4 Reflector alignment.9
5.5 Detector .10
5.6 Sample station . .10
5.7 Control unit .10
6 Calibration and quality control .10
6.1 Angle inspection .10
6.2 Energy calibration .10
6.3 Calibration of the element sensitivities .11
6.4 Inspection of the sample excitation . 12
6.5 Inspection of the element detection . 12
7 Spectra analysis and Reporting .12
7.1 Spectra Processing . . 12
7.2 Reporting Spectra . 13
8 Samples .13
9 Qualitative and quantitative analysis . 14
9.1 Qualitative analysis .14
9.2 Quantitative analysis .14
9.2.1 Methods of quantitative analysis .14
9.3 Preparation of a measurement for quantitative analysis . 15
9.4 Procedure of a quantitative analysis by the element-specific sensitivity method
(internal standard addition) .16
9.5 Verification of quantitative TXRF measurements .17
9.6 Traceability in TXRF .17
Annex A (informative) Measurement angles in TXRF, background correction, peak correction,
spectrum deconvolution .18
Annex B (informative) Round-robin test for verification of the precision and accuracy of TXRF
spectroscopy .21
Bibliography .22

iii
Foreword
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This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee
SC 10, X-ray Reflectometry (XRR) and X-ray Fluorescence (XRF) Analysis.
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iv
Introduction
Through general technical developments, total reflection X-ray fluorescence analysis (TXRF) has been
developed into a robust independent physical method of instrumental analytical chemistry. TXRF is
a distinct multi-element micro-method and a method of surface analysis. It is used for the simultaneous
qualitative detection of the elements and quantification of the element masses. Notably, only small
quantities of material are used for the analysis to benefit from all the advantages inherent to the procedure
and thus to achieve correct analysis values. TXRF is used alongside other atomic spectroscopic methods,
such as atomic absorption spectrometry (AAS) or inductively coupled plasma-based techniques (ICP-AES
and ICP-MS) that are also established in the field of element analysis. In addition, TXRF is used in surface
analysis and complements techniques such as Auger electron spectroscopy (AES), Rutherford backscattering
spectrometry (RBS) or secondary ion mass spectrometry (SIMS). The rapid and in part non-destructive
measurement process of a TXRF configuration allows screening or qualitative analysis of unknown flat,
film-like and particulate samples and is therefore a valuable addition to other analytical techniques.
The main difference between TXRF and conventional X-ray fluorescence spectrometry (XRF) is the efficient
way to e
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