Читать книгу X-Ray Fluorescence in Biological Sciences - Группа авторов - Страница 75

X‐ray fluorescence (XRF) analysis is a method of qualitative and quantitative multi‐elemental detection which is non‐destructive. It is a nuclear analytical instrumental technique designed based on the determination of characteristic fluorescent radiation of a particular element. A suitable point source is applied to de‐excite the inner shell vacancies of sample elements by means of radiation. Of the numerous variants of XRF analysis, two major approaches are wavelength dispersive‐XRF (WDXRF) and energy dispersive‐XRF (EDXRF). They are distinguished from each other by the type of detector used to detect emission spectra, which is particular for each element. The characteristic wavelength of emitted X‐rays from elements obtained by the use of a diffracting crystal is the main focus of WDXRF whereas EDXRF relies on direct measurement of the energy of the X‐rays by collecting ionization produced in a suitable detecting medium. After the emergence of silicon drift detectors (SDD), EDXRF became the most widely used of the two. As compared with EDXRF, WDXRF is quite expensive and has few applications for testing materials in the steel or ceramics industries. In recent years, EDXRF has led over WDXRF and is a powerful tool for elemental analysis to determine major, minor, and trace elements in biological samples. The sample preparation for the EDXRF technique is much easier and therefore less prone to contamination. Generally, no chemicals are used, so system loss is relatively very small. A special feature of EDXRF is that only a very small amount of sample is required, which is in the range mg‐μg of a material. Hence it is suitable for clinical measurement of toxic elements in human body tissue, as the collection of human tissue in large volume/quantity is a big problem. Arsenicosis and autism spectrum disorder (ASD) are the conditions which are associated with the accumulation of toxic elements arsenic (As) and lead (Pb) in the human body respectively. Determining their concentrations in human tissues can give a clear picture of their presence (qualitatively and quantitatively) and evaluate their association with those diseases. In this chapter, EDXRF techniques for the determination of As concentration in human scalp hair for the diagnosis of arsenicosis, and determination of Pb concentration in whole blood samples for evaluating the relationship between lead exposure and blood lead concentration as a function of ASD have been discussed.