Speciation Analysis of Osmium(VIII) and Osmium(IV) by UV‐VIS Spectrophotometry Using Quercetin as the Reagent

The UV‐VIS spectrophotometric methods for the determination of Os(VIII) (as OsO4) and Os(IV) (as OsCl6 2− complex) in their mixtures were developed. Quercetin (Q), a flavonoid compound, was used as a chromogenic reagent. Both direct and derivative spectrophotometry can be employed for the determination of Os(VIII). The calculation of the first‐derivative spectrum of the examined mixture and the use of the signal at 285.1 nm allows reaching a better detection limit (0.01 µg mL−1 Os) as compared with direct spectrophotometry (0.1 µg mL−1 Os). Relative standard deviations of the results are in the range of 0.87%–4.65% and 0.45%–1.15% for direct and derivative mode, respectively. Selective redox reaction of OsO4 with Q under the conditions used (0.05 M HCl, 1×10−4 M Q, 15 min heating at 70°C) makes the basis of its determination in mixtures with the OsCl6 2− complex. Quercetin does not react with the OsCl6 2− complex. The signals of the OsCl6 2− complex can be isolated from the examined mixtures by the calculation of the third‐order derivative spectra and the use of the values at 340.0 nm. The effectiveness of the reduction of OsO4 in chloride solutions has been studied by the developed method.