Noninvasive Quantitative Chromium(III) Speciation in Neat Solid Mixtures by Extended X-ray Absorption Fine Structure Spectroscopy

Abstract

A procedure that uses extended X-ray absorption fine structure (EXAFS) spectroscopy for quantitative chromium(III) speciation in neat solid mixtures is described. The procedure uses the full, filtered EXAFS, e.g., 4 ≤ k ≤ 12 Å⁻¹, rather than the smaller k-range associated with a single coordination sphere. Concentration is determined by a simple correlation of full, filtered EXAFS of standards with full, filtered EXAFS of mixtures. Under optimized conditions, calibration curves for mixtures of Cr₂O₃ and Cr(NO₃)₃·9H₂O have slopes of 1.002, respective intercepts of −0.7% and 0.5%, and correlation coefficients of 0.9991. Fluorescence EXAFS from mixtures must be compared to fluorescence EXAFS from standards, and the matrices and thicknesses of standards and mixtures must be closely matched. Transmission EXAFS of standards must be obtained to correct for self-absorption effects.