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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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 excite the material to be examined to fluoresce which is achieved by a special geometrical arrangement in the spectrometer. The spectral background is drastically reduced, the fluorescence intensity increased resulting in a significant enhancement of the signal to noise ratio. Special sample treatment and sample presentation are required for this purpose. If these boundary conditions are met, TXRF achieves a high degree of accuracy and repeatability of the analyses, although a simplified calibration and quantification is used. The detection limits currently achievable with TXRF are approximately 10⁻¹² g or 10¹⁰ atoms/cm² and are thus orders of magnitude lower than for XRF. The relative element concentrations are, depending on the matrix or the main components of the sample and for the elements to be examined, between 0,1 % and up to 10⁻⁹ for the low concentrations.

This document describes the physical principles and instrumentation required for TXRF analysis assuming that the conditions for total reflection are met, without referring to the samples’ specificity. As a demonstration of the good reproducibility of the TXRF instruments, data from a round‑robin test performed using centrally prepared and optimized samples are presented (see Annex B).

Other standards focussing on specific case studies and procedures are available for silicon wafers (see ISO 14706 and ISO 17331 ), environmental and biological samples (see ISO/TS 18507 ), and water ( ISO 20289 ).

1 Scope

The document provides the physical principles and specifies instrumental requirements for total reflection X‑ray fluorescence analysis (TXRF) spectrometers. This document specifies general procedures for calibration, method development and verification of TXRF measurements and quality control.

The document describes measurements with TXRF conditions having a fixed glancing angle below the critical angle of total reflection and considerably enhanced excitation radiation intensity. Although certain definitions of grazing incidence geometry are shown for clarification, this document is not applicable to measurement setups working under such conditions.

2 Normative references

3 Terms, definitions and abbreviations

3.1 Abbreviated terms

4 Physical background of TXRF

4.1 General

4.2 Definition of angle and X‑ray path in TXRF geometry

4.3 Beam projection

4.4 X‑ray standing waves (XSW)

4.5 Fluorescence intensity

5 Instrumental requirements

5.1 Description of various possible TXRF measurement setups

5.2 Beam conditioning

5.3 Reflector (sample carrier)

5.4 Reflector alignment

5.5 Detector

5.6 Sample station

5.7 Control unit

6 Calibration and quality control

6.1 Angle inspection

6.2 Energy calibration

6.3 Calibration of the element sensitivities

6.4 Inspection of the sample excitation

6.5 Inspection of the element detection

7 Spectra analysis and Reporting

7.1 Spectra Processing

7.2 Reporting Spectra

8 Samples

9 Qualitative and quantitative analysis

9.1 Qualitative analysis

9.2 Quantitative analysis

9.3 Preparation of a measurement for quantitative analysis

9.4 Procedure of a quantitative analysis by the element‑specific sensitivity method (internal standard addition)

9.5 Verification of quantitative TXRF measurements

9.6 Traceability in TXRF

Bibliography