Experimental test of the Fundamental Parameter equation using resin doped with Fe, Cu, Zn, As, and Se.*

X-ray fluorescence (XRF) is a nondestructive analytical technique able to detect chemical elements with atomic numbers larger than that of Na in concentrations of a few µg/g or lower. Biological XRF investigations of thin tissue samples using small X-ray beams can probe their 2D microscopic distribution of chemical elements. Conversion of experimentally-acquired signals into elemental concentrations (ECs) can enhance the scientific value of such studies and facilitates quantitative comparisons among different investigations. In our study, five resin samples of various thicknesses in the 3.7 to 6.3 mm were doped with equal ECs of Fe, Cu, Zn, As, and Se: 0.0, 9.96, 18.77, 26.7, 33.9, and 40.9 µg/g. Fundamental Parameter equation was applied to the spectrometric XRF-to-scatter ratio data to compute ECs and compare them with the known values. X-ray beam photon fluence rate knowledge is not required in this approach. Computed ECs matched their known values within experimental uncertainties. Data analysis, however, indicated that external XRF signal contaminations for Fe and As complicated interpretation of the results.