X-ray Fluorescence Analysis of Cr⁶⁺ Component in Mixtures of Cr₂O₃ and K₂CrO₄

Abstract

X-ray fluorescence analysis using Cr K_α spectra was applied to the determination of the mixing ratio of Cr⁶⁺ to (Cr⁶⁺ + Cr³⁺) in several mixtures of K₂CrO₄ and Cr₂O₃. Because the powder of K₂CrO₄ contained large particles that were more than 50 μm in diameter, it was ground between a pestle and a mortar for about 8 h. The coarse particles still remaining were removed by using a sieve with 325-mesh (44 μm) in order to reduce the difference in absorption effects between emissions from Cr⁶⁺ and those from Cr³⁺. The mixing ratio, K₂CrO₄/(K₂CrO₄ + Cr₂O₃), of the five mixtures investigated is 0.50, 0.40, 0.20, 0.10, and 0.05 in weight, respectively. Each spectrum obtained was analyzed by decomposing it into two reference spectra, those of the two pure materials, K₂CrO₄ and Cr₂O₃, with a constant background. The results for the mixtures containing K₂CrO₄ of more than 20 wt% are that the relative deviation from the true value is less than ∼5%. On the other hand, when the content of K₂CrO₄ decreases to less than 10 wt%, the relative deviation gets so large as 20 – 25%. The error coming from a peak separation of spectrum involved in our results were estimated by applying our method to five sets of data for each mixture computationally generated, taking into account the uncertainty in total counts of real measurements.