Spectrophotometric Determination of Os(VIII) with Nitroso R Salt as Chromogenic Reagent

Résumé

Several methods have been reported for the spectrophotometric determination of osmium with various chromogenic reagents. Some of these reagents react slowly with osmium and the conditions for obtaining reproductibile colours are usually empirical.
In this context, a simple and sensitive spectrophotometric method for the determination of trace amounts of osmium(VIII) using disodium-1-nitroso-2-hydroxynaphthalene-3,6-disulphonate (Nitroso R salt) is described. The method is based on the formation of an Os–Nitroso R salt complex which exhibits two different colours as function of pH. Linear calibration graphs are obtained up to 60 μg/mL of the analyte at pH = 4.8. The stoichiometry of the complex is found to be 1: 4 by mole ratio method. The method is optimized and different analytical parameters were evaluated. For instance, the calculated values for the molar absorptivity are of 3.645.10³ L/mol.cm (pH = 0; λ = 550 nm) and 1.695.10³ L/mol.cm (pH = 4.8; λ = 510 nm), respectively. The proposed method should be valuable for the determination of osmium(VIII) with good accuracy and precision.