X-Ray Spectrometry - Survival-training.info

2 CONSIDERING THE ROLE OF X-RAY SPECTROMETRY IN CHEMICAL ANALYSIS AND OUTLINING THE VOLUMElacking in XRS and scientists began to have someambivalent opinions regarding the future role ofXRS in analytical chemistry. One could wonderwhether, in spite of remarkably steady progress,both instrumental and methodological, XRS hadreached a state of saturation and consolidation,typical for a mature and routinely used analysistechnique.In the meantime, XRF had indeed developedinto a well-established and mature multi-elementtechnique. There are several well-known key reasonsfor this success: XRF is a universal techniquefor metal, powder and liquid samples; it is nondestructive;it is reliable; it can yield qualitative andquantitative results; it usually involves easy samplepreparation and handling; it has a high dynamicrange, from the ppm level to 100 % and it can, insome cases, cover most of the elements from fluorineto uranium. Accuracies of 1 % and better arepossible for most atomic numbers. Excellent datatreatment software is available allowing the rapidapplication of quantitative and semi-quantitativeprocedures. In the previous decades, somewhatnew forms of XRS, with e.g. better sensitivityand/or spectral resolution and/or spatial resolutionand/or portable character, had been developed.However, alternative and competitive more sensitiveanalytical techniques for trace analysis had, ofcourse, also been improved; we have seen the riseand subsequent fall of atomic absorption spectrometryand the success of inductively coupled plasmaatomic emission and mass spectrometry (ICP-AESand ICP-MS) in the last two decades.Since 1990, however, there has been dramaticprogress in several sub-fields of XRS, and inmany aspects: X-ray sources, optics, detectorsand configurations, and in computerisation andapplications as well. The aim of the followingchapters in this book is precisely to treat the latestand often spectacular developments in each ofthese areas. In principle, all references will pertainto the last 5–6 years. Many of the chapters willhave a high relevance for the future role of XRSin analytical chemistry, but certainly also for manyother fields of science where X-rays are of greatimportance. The following sections in this chapterwill give a flavour of the trends in the positionof different sub-fields of XRS based e.g. on therecent literature and will present the outline ofthis volume.1.1.2 THE ROLE AND POSITION OFXRS IN ANALYTICAL CHEMISTRYAn attempt has been made to assess the recenttrends in the role and position of XRS based on aliterature survey (see also Injuk and Van Grieken,2003) and partially on personal experience andviews. For the literature assessment, which coveredthe period from January 1990 till the end ofDecember 2000, a computer literature search onXRS was done in Chemical Abstracts, in orderto exclude (partially) the large number of XRSpublications on astronomy, etc.; still, it revealedan enormous number of publications. Figure 1.1.1shows that the volume of the annual literature onXRS, cited in Chemical Abstracts, including allarticles having ‘X-ray spectrometry/spectroscopy’in their title, is still growing enormously and exponentially.During the last decade, the number ofpublications on XRS in general has nearly doubled;in 2000, some 5000 articles were published,versus 120 annually some 30 years ago. As seenin Figure 1.1.2, XRS in general seems more alivethan ever nowadays.However, the growth of the literature on specificallyXRF is much less pronounced: from about500 articles per year in 1990 to about 700 in 2000,still a growth of 40 % in the last decade. While in1990 it looked like XRF had reached a state of saturationand consolidation, newer developments inthe 1990s, e.g. the often-spectacular ones describedin the other chapters of this volume, have somehowcountered such fears. It is a fact that WDXRFremains the method of choice for direct accuratemulti-element analysis in the worldwide mineraland metallurgy industry. For liquid samples, however,the competition of ICP-AES and ICP-MSremains formidable. It is striking that, while thereare still many more WDXRF units in operationaround the world than EDXRF instruments, thenumber of publications dealing with WDXRF isabout five times lower. This clearly reflects thepredominant use of the more expensive WDXRF