K-shell X-ray fluorescence measurements of arsenic depth-dependent concentration in polyester resin discs using the fundamental parameter method

In the realm of X-ray fluorescence (XRF) applications, inhomogeneous distribution of an element can occur as a function of depth within a sample. An example is the measurement of arsenic in skin; arsenic binds with non-uniformly distributed keratin. In this paper, an XRF signal equation based on the fundamental parameter (FP) method, which explicitly takes into account the depth dependence of the elemental concentration, was developed. The formalism was experimentally verified for two-disc resin stacks with different arsenic concentrations.