Chapter 7: Determination of Trace Elements Using X-ray Fluorescence (XRF) Wavelength Dispersive (WD) and Energy Dispersive (ED) Check Access

X-ray radiation (12–0.6 Å i.e., 1 to 20 keV) normally generated by an X-ray tube (operating at a potential of between 10–100 kV) ionizes an atom of an element on interaction. The atom loses an electron from its orbital near to the nucleus and is de-excited by emitting fluorescence X-ray radiation characteristic of the element. Samples containing the element are prepared in the form of pressed powder pellets or fused glass discs for excitation to reduce the matrix effect. The wide dynamic range of the method makes it easy to determine major, minor and trace levels of chemical twins like Zr–Hf ratios; Rb, Sr, Ba; Nb–Ta; U, Th in several complex minerals, rare earths; nonmetals like S, P, Se, halogen, by selecting suitable lines/energies by WDXRF or EDXRF besides TRXRF and other hyphenated techniques based on X-rays. Total reflection XRF, a multi-element technique (with a Si (Li)-detector) for determination of trace metals (right from C to Pu at ppb levels), a highly surface sensitive technique, needs a wafer like polished surface, utilises extremely low angle (0.05–0.5°, below the critical angle for the substrate containing the sample) X-ray excitation to reduce Rayleigh and Compton scattering.