Conversion of Chromium(III) Propionate to Chromate/dichromate(VI) by the Advanced Oxidation Process. Pretreatment of a Biomimetic Complex for Metal Analysis

The use of H₂O₂ and UV irradiation to remove organic ligands in a chromium(III) complex for the subsequent chromium analysis is reported. The Advanced Oxidation Process (AOP) using a 5.5-W UV lamp, H₂O₂ and Fe²⁺/Fe³⁺ as catalyst (photo Fenton process) was found to give complete and quantitative Cr(III) → Cr(VI) conversion and removal of ligands in chromium(III) propionate Cr₃O(O₂CCH₂CH₃)₆(H₂O)₃]NO₃, a biomimetic chromium species, as subsequent chromium analyses by the 1,5-diphenylcarbazide method and atomic absorption revealed. The current process eliminates the need for mineralization and/or dissolution of the matrix in order to remove the organic ligand, the traditional pretreatments of a sample for metal analysis. Studies to optimize the conditions for the oxidation processes, including the use of Fe²⁺/Fe³⁺ catalyst, length of UV irradiation, H₂O₂ concentration, pH, power of UV lamp, and reactor size, are reported.