X-Ray Fluorescence Spectroscopy for Laboratory Applications
Description
This book focuses on the practical aspects of X-ray fluorescence (XRF) spectroscopy and discusses the requirements for a successful sample analysis, such as sample preparation, measurement techniques and calibration, as well as the quality of the analysis results.
X-Ray Fluorescence Spectroscopy for Laboratory Applications begins with a short overview of the physical fundamentals of the generation of X-rays and their interaction with the sample material, followed by a presentation of the different methods of sample preparation in dependence on the quality of the source material and the objective of the measurement. After a short description of the different available equipment types and their respective performance, the book provides in-depth information on the choice of the optimal measurement conditions and the processing of the measurement results. It covers instrument types for XRF; acquisition and evaluation of X-Ray spectra; analytical errors; analysis of homogeneous materials, powders, and liquids; special applications of XRF; process control and automation.
* An important resource for the analytical chemist, providing concrete guidelines and support for everyday analyses
* Focuses on daily laboratory work with commercially available devices
* Offers a unique compilation of knowledge and best practices from equipment manufacturers and users
* Covers the entire work process: sample preparation, the actual measurement, data processing, assessment of uncertainty, and accuracy of the obtained results
X-Ray Fluorescence Spectroscopy for Laboratory Applications appeals to analytical chemists, analytical laboratories, materials scientists, environmental chemists, chemical engineers, biotechnologists, and pharma engineers.
Reviews / Votes
X-ray fluorescence spectroscopy for laboratory applications is a strongly recommended, high-quality monograph in the field of X-ray spectroscopy. [?] [I]t is a unique resource for practitioners and scientists.Kerstin Leopold in Analytical and Bioanalytical Chemistry (29.07.2021)
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Persons
Dr. Jörg Flock is Head of the Central Laboratory of ThyssenKrupp Stahl AG and well-versed with different analytical techniques, in particular with x-ray fluorescence spectroscopy. He has extensive practical experience of using this technique for the analysis of samples with different qualities and the interpretation of the acquired results.
Michael Haller has been using X-rays as an analytical tool for over thirty years, first in X-ray crystallography, then later in the development and application of polycapillary X-ray optics. Further he has developed new applications for coating thickness instruments. In 2018 he became co-owner of CrossRoads Scientific, a company specializing in the development of analytical X-ray software.
Content
List of Abbreviations and Symbols xix
About the Authors xxiii
1 Introduction 1
2 Principles of X-ray Spectrometry 7
2.1 Analytical Performance 7
2.2 X-ray Radiation and Their Interaction 11
2.3 The Development of X-ray Spectrometry 21
2.4 Carrying Out an Analysis 26
3 Sample Preparation 31
3.1 Objectives of Sample Preparation 31
3.2 Preparation Techniques 32
3.3 Preparation of Compact and Homogeneous Materials 39
3.4 Small Parts Materials 41
3.5 Liquid Samples 55
3.6 Biological Materials 58
3.7 Small Particles, Dust, and Aerosols 59
4 XRF Instrument Types 61
4.1 General Design of an X-ray Spectrometer 61
4.2 Comparison of Wavelength- and Energy-Dispersive X-Ray Spectrometers 63
4.2.5 Radiation Flux 75
4.3 Type of Instruments 80
4.4 Commercially Available Instrument Types 98
5 Measurement and Evaluation of X-ray Spectra 99
5.1 Information Content of the Spectra 99
5.2 Procedural Steps to Execute a Measurement 101
5.3 Selecting the Measurement Conditions 102
5.4 Determination of Peak Intensity 112
5.5 Quanti¿cation Models 117
5.6 Characterization of Layered Materials 133
5.7 Chemometric Methods for Material Characterization 140
5.8 Creation of an Application 143
6 Analytical Errors 149
6.1 General Considerations 149
6.2 Types of Errors 156
6.3 Accounting for Systematic Errors 159
6.4 Recording of Error Information 164
7 Other Element Analytical Methods 167
7.1 Overview 167
7.2 Atomic Absorption Spectrometry (AAS) 168
7.3 Optical Emission Spectrometry 169
7.4 Mass Spectrometry (MS) 172
7.5 X-Ray Spectrometry by Particle Excitation (SEM-EDS, PIXE) 173
7.6 Comparison of Methods 175
8 Radiation Protection 177
8.1 Basic Principles 177
8.2 E¿ects of Ionizing Radiation on Human Tissue 178
8.3 Natural Radiation Exposure 179
8.4 Radiation Protection Regulations 181
8.4.1 Legal Regulations 181
9 Analysis of Homogeneous Solid Samples 183
9.1 Iron Alloys 183
9.2 Ni?Fe?Co Alloys 188
9.3 Copper Alloys 189
9.4 Aluminum Alloys 191
9.5 Special Metals 192
9.5.1 Refractories 192
9.6 Precious Metals 195
9.7 Glass Material 199
9.8 Polymers 203
9.9 Abrasion Analysis 209
10 Analysis of Powder Samples 213
10.1 Geological Samples 213
10.2 Ores 216
10.3 Soils and Sewage Sludges 221
10.4 Quartz Sand 223
10.5 Cement 223
10.6 Coal and Coke 227
10.7 Ferroalloys 230
10.8 Slags 235
10.9 Ceramics and Refractory Materials 237
10.10 Dusts 239
10.11 Food 242
10.12 Pharmaceuticals 245
10.13 Secondary Fuels 246
11 Analysis of Liquids 253
11.1 Multielement Analysis of Liquids 254
11.2 Fuels and Oils 255
11.3 Trace Analysis in Liquids 261
11.4 Special Preparation Techniques for Liquid Samples 263
12 Trace Analysis Using Total Re¿ection X-Ray Fluorescence 267
12.1 Special Features of TXRF 267
12.2 Sample Preparation for TXRF 269
12.3 Evaluation of the Spectra 271
12.4 Typical Applications of the TXRF 274
13 Nonhomogeneous Samples 287
13.1 Measurement Modes 287
13.2 Instrument Requirements 288
13.3 Data Evaluation 290
14 Coating Analysis 291
14.1 Analytical Task 291
14.2 Sample Handling 292
14.3 Measurement Technology 293
14.4 The Analysis Examples of Coated Samples 294
15 Spot Analyses 313
15.1 Particle Analyses 313
15.2 Identi¿cation of Inclusions 318
15.3 Material Identi¿cation with Handheld Instruments 318
15.4 Determination of Toxic Elements in Consumer Products: RoHS Monitoring 324
15.5 Toxic Elements in Toys: Toys Standard 328
16 Analysis of Element Distributions 331
16.1 General Remarks 331
16.2 Measurement Conditions 332
16.3 Geology 333
16.4 Electronics 342
16.5 Archeometric Investigations 344
16.6 Homogeneity Tests 350
17 Special Applications of the XRF 355
17.2 Chemometric Spectral Evaluation 358
17.3 High-Resolution Spectroscopy for Speciation Analysis 361
18 Process Control and Automation 367
18.1 General Objectives 367
18.2 O¿-Line and At-Line Analysis 369
18.3 In-Line and On-Line Analysis 376
19 Quality Management and Validation 379
19.1 Motivation 379
19.2 Validation 380
Appendix A Tables 387
Appendix B Important Inf
1
Introduction
X-ray spectrometry has been known as a method for element analyses for more than 70 years and can be regarded as a routine method since the 1960s. This means that there is a broad range of instruments available, and numerous analytical tasks are carried out routinely by X-ray fluorescence (XRF) analysis. For example, XRF is used for the characterization of metallic or geological materials or for analyses of solid or liquid fuels despite the fact that other elemental analytical methods have been developed and are readily available for these applications. Among them are optical emission spectrometry with excitation both by sparks and by inductively coupled plasmas and mass spectrometry. The high importance of using XRF is due to the fact that one can achieve very high precision over a wide concentration range. XRF also requires little effort with sample preparation and the method can be automated.
Especially in the last 15-20 years, XRF has experienced a new boom mainly because the technology has further developed, and new fields of applications could be opened up. These include, among others, the analysis of layered materials and high-resolution position-sensitive analysis. This was made possible by the availability of new components for X-ray spectrometers.
The development of high-resolution energy-dispersive detectors with good count rate capability now allows precision measurements also with energy-dispersive spectrometers. The simultaneous detection of a wide energy range over a large solid angle made possible with these detectors allows not only short measuring times but also special excitation geometries. It is therefore now possible to achieve higher sensitivities in the detection of traces; further, the fluorescence radiation of small surface areas can be detected with sufficient intensity.
The development of various X-ray optics allows shaping of the primary X-ray beam and thus the concentration of high excitation intensity on small sample surfaces; this development was the key to opening up new applications in the field for a spatially resolved analysis.
These developments have significantly expanded the range of applications of XRF analysis.
However, the most important influence in the further development of XRF into a routine method was the advances in data processing technology. These made it possible to automate instrument control as well as the evaluation of measurement data. Not only was it possible to reduce subjective influences by a manual operator but also the processes during instrument control and measurement data acquisition could largely be automated and made more effective. The evaluation of the measurement data, such as the peak area calculation in case of overlapping peaks, or the calculation procedures for the quantification could be expanded and significantly refined by the available computing power.
These improvements have been particularly important because X-rays strongly interact with the sample matrix, which requires complex correction procedures. Nevertheless, in contrast to other analytical methods, the physics of these interactions is very well understood and can be exactly modeled mathematically. Consequently, in principle, standard-less analysis is possible, which again requires a high computing effort.
As a result of these developments, new methodical possibilities for XRF emerged, combined with an expansion of their field of applications. For this reason, it seems to be meaningful to carry out an up-to-date compilation of the applications currently being processed by XRF, in combination with a discussion of both the necessary sample preparation and instrument-related efforts and the achievable analytical performance. There are several very good books available, which however, due to their date of publication, have not been able to take into account the developments of the last 15-20 years (Erhardt 1989; Hahn-Weinheimer et al. 2012) or they do not adequately address frequently used routine applications, in particular in industrial analyses (Beckhoff et al. 2006; van Grieken and Markowicz 2002).
The goal of this book is to focus on the practical aspects of the various applications of XRF. This leads to the discussion of the requirements necessary for the analysis of the very different sample qualities, such as the type of sample preparation, the available measurement technique or the required calibration samples, as well as the type and quality of the results to be expected with these efforts. This appeared to be important, in particular, because XRF is often used in many laboratories, but methodical studies are carried out only in very few of them.
This leads to the application aspects often not being understood very well. Consequently, the analytical results are accepted without scrutinizing the influence of sample state, preparation methods, and measurement parameters. This becomes especially true because complete results are often available as the outcome of an instrumental analysis and their quality cannot be correctly comprehended.
In order to assure the quality of the applications and their results, the analyst must critically question all aspects of the test method. For this purpose, a basic understanding of the influences of sample condition, preparation methods, measurement parameters, and evaluation models used on the quality of the analytical result is imperative.
Therefore, we are deliberately focusing on the daily laboratory work with commercially available instruments. On the other hand, the interesting but not routine applications of the method utilizing synchrotron radiation excitation are not addressed. Nevertheless, methodical developments obtained on a synchrotron are often incorporated into laboratory analysis, such as micro-X-ray fluorescence (µ-XRF) or applications with grazing beam geometry. However, this book treats only laboratory applications. If any of these newly developed methods have been implemented into special laboratory instruments these are also presented as examples.
Despite the focus on the various applications, a brief introduction to the fundamentals of X-ray spectrometry and a comprehensive presentation of the basic steps for a complete analysis are required in order to be able to relate in the following discussion of the individual applications.
The book therefore starts with a discussion of the analytical capability of X-ray spectrometry in Chapter 2. The most important relations that describe the generation of the characteristic radiation are presented, and the individual steps in the execution of an analysis follow, along with a brief characterization of their influence on the analysis result. Deeper descriptions of the physical bases are comprehensively given in other publications (e.g. Erhardt 1989; Hahn-Weinheimer et al. 2012; van Grieken and Markowicz 2002; Beckhoff et al. 2006).
In Chapter 3, the various sample preparation procedures typical for X-ray spectrometry are presented and their influence on the precision and trueness of the analyses is discussed. Even though the sample preparation is generally regarded as being very simple for XRF, it is important to carry it out carefully, appropriate to the expectations of the analysis result.
In Chapter 4, the different types of X-ray spectrometers are discussed. On the one hand, the general differences and application characteristics of wavelength-dispersive and energy-dispersive instruments are examined; on the other hand, the different instrument types as well as the instruments currently available on the market are presented.
In Chapter 5, the essential steps for the measurement of a spectrum are reviewed, in particular, the optimum selection of the measurement parameters and the steps for the evaluation of the measured data. The first step is the determination of the intensities of the fluorescence peaks, where different procedures are used for wavelength- and energy-dispersive spectrometers. Then quantification models and factors concerning the consideration of matrix interaction, both in the analysis of homogeneous samples and in the characterization of layers, are presented. Here, a comprehensive and detailed description of the theory of X-ray spectrometry is not required, since a series of detailed papers are available (see, for example, Hahn-Weinheimer et al. 2012; Jenkins et al. 1981; Lachance and Claisse 1994; Mantler 2006) and only very few new ideas have been added in the last few years. In this chapter, further possibilities for the evaluation of spectra are presented, in which the individual spectral components are not considered separately, but the spectrum as a whole is evaluated by means of chemometric methods.
Chapter 6 is devoted to the discussion of the classification, determination, and evaluation of errors. The achievable analytical precision of XRF is determined by the errors. In addition to the traditional treatment of errors with the Gaussian error model, the principle of measurement uncertainty is also discussed. This chapter is intended to qualify the expectations of an analytical result.
In Chapters 7 and 8, a brief comparison is made with other element analysis methods, in particular atomic absorption and emission spectrometry as well as mass spectrometry. The fundamentals of radiation protection when dealing with X-ray radiation, in particular when carrying out X-ray analysis experiments, are compiled as well.
Based on these fundamentals, various applications...
