Determination of trace elements in light element matrices by x-ray fluorescence spectrometry with incoherent scattered radiation as an internal standard

Abstract

A method for the direct determination of trace elements in light element matrices is described. It takes advantage of the fact that the incoherent mass scattering coefficient for 17.4 keV Mo K..cap alpha.. radiation is relatively constant for the elements Li(Z = 3) ..-->.. Ca (Z = 20). Consequently, incoherent scattered Mo K..cap alpha.. excitation radiation, corrected for matrix absorption, can serve as an internal standard which compensates for variations in sample mass, x-ray tube output, and sample geometry. Samples of approx. 0.5 g are prepared in the form of thin specimens (approx. 0.08-cm thick) in a cell between two 0.0006-cm thick polypropylene windows. Standardization for most elements is achieved using standard aqueous solutions diluted to approx. 100 ppM. Data obtained from simultaneous transmission measurements for several x-ray energies are used to calculate matrix absorption corrections. For 15-min analysis periods, results are typically accurate to within +-10% when x-ray counting statistics are not the limiting factor. Sensitivities of 2 ppM or better are realized for 16 of the 22 elements determined (Ti ..-->.. Zr, Hg, Pb, Th, and U). 7 figures, 7 tables.