X-Ray Fluorescence Determination of FeII/Fetotal Ratios in Sediments and Soils

The two most common oxidation states of iron can be determined by wavelength-dispersive X-ray fluorescence spectrometry relatively fast with an accuracy comparable to that of alternative methods. Main advantages for the analysis of sediments and soils are that organic matter does not interfere and solid samples can be analysed directly with minimal preparation effort. The limited availability of appropriate reference materials with certified data on their ferrous iron content turned out to be the major obstacle to implementing the method. For this reason and because no influence of the analysed geological materials on the intensity ratios of the closely adjacent Fe Kβ₅ / Fe Kβ_1,3 lines became evident, several rock types were selected in addition to sediments and soils to broaden and improve the calibration. Nevertheless, most reference data for calibration had to be determined by ⁵⁷Fe Mössbauer spectroscopy. Plotting Fe Kβ₅/Fe Kβ_1,3 intensity ratios versus w FeO/w Fe₂O₃^total ratios resulted in a correlation with R² = 0.962 for the linear regression of all calibration data.