Dependence of analytical signal on the concentration of analyte in X-ray spectral analysis

Abstract

The dependence of the intensity of analytical signals on the element concentrations expressed in weight percentages I(c) and atomic percentages I(a) in X-ray spectrochemical analysis is considered. It was shown that the change-over from the dependence I(a) to the dependence I(c), which took place in the 1950s, had no theoretical grounds, was based on an incorrect application of the concepts of density and Avogadro’s constant, and was accepted because of practical convenience. In the dependence I(c), the calibration characteristics becomes more complex; it requires corrections for matrix effects, even if these effects are absent. Analytical data published in weight percentages and obtained in the analysis of various samples by conventional X-ray fluorescence analysis (XRFA), X-ray radiometric analysis with an energy-dispersive spectrometer, absorption analysis, and electron probe microanalysis are recalculated into atomic percentages. These results and the data obtained by the author in the analysis of alloys and steels demonstrate a correlation between the intensity of characteristic lines and the atomic concentration of the components. If the calibration curve is based on I(a), a linear dependence over a wide range or the entire concentration range is observed in the majority of systems, the number of the necessary reference standard materials sharply decreases (to one), the sensitivity coefficient increases, and the corrections for matrix effects decrease or the necessity for them disappears.