Calculation of depth-dependent elemental concentration with X-ray fluorescence using a layered calibration method

Depth-dependent elemental concentration can be assessed using either multiple-angle or confocal X-ray fluorescence (XRF) measurements. This work presents a different approach based on a layered calibration method. The depth-dependent elemental concentration was modeled as multiple layers of uniform elemental concentrations. The unknown elemental concentration in each layer can be calculated using a single-angle XRF measurement, layered calibration data, and a priori knowledge of the concentration behavior as a function of depth. The method was verified using a commercial portable X-ray spectrometer and four-layer stacks of polyester resin discs doped with various concentrations of arsenic. This approach is particularly suitable for quantitative in vivo measurements of arsenic and selenium concentrations in the human skin since minimal ionizing radiation exposure constrains the number of XRF measurements.