WD-XRF technique for speciation of iron and quantification of its oxidation states in geological samples using L-series of iron X-ray spectrum

Wavelength dispersive X-ray fluorescence (WD-XRF) spectrometry is a fast and widely used technique for elemental analysis of geological samples from Na to U. However, it has seldom been applied for quantitative determination of oxidation states of elements in complex matrices. In this study, we present a method to determine the oxidation states of iron in geological samples by WD-XRF. We used the FeLα_1,2 fluorescence line as a tool for iron speciation and Fe(II)/Fe^total ratio determination. We found that the normalized intensity (peak height) of FeLα_1,2 fluorescence line was linearly correlated with the spin multiplicity (2S + 1) of ferrous and ferric content in the samples. To account for the matrix effects of chemical environment (matrix and chemical bonding) on FeLα_1,2 fluorescence line, we introduced a chemical index factor (μ) that enabled accurate determination of Fe(II)/Fe^total ratio in different types of geological samples. The method was validated using international certified reference materials and their mixtures and obtained promising results, with only 6 out of 55 determinations showing relative error more than 5% of the certified values.