Sequential separation and spectrophotometric determination of osmium and platinum with 5-chloro-2-hydroxythiobenzhydrazide.

Osmium was determined spectrophotometrically after coprecipitation with 5-chloro-2-hydroxythiobenzhydrazide at room temperature in the pH range 2.5-5.0 and collection on microcrystalline naphthalene. Beer's law was obeyed in the concentration range 1.8-14.4 ppm of osmium in a chloroform solution at 510 nm. The molar absorptivity and Sandell sensitivity were 1.056 x 10(4) l mol(-1) cm(-1) and 0.018 ppm, respectively. Six replicate analyses of a solution containing 7.2 ppm of osmium gave a mean absorbance of 0.405 with a standard deviation of 0.013 and a relative standard deviation of 0.92%. The complex was stable for over 72 h. The metal-to-ligand ratio in the complex was 1:2. Interference from various ions was studied, and the method was applied to the determination of osmium in various synthetic mixtures containing commonly associated metals and corresponding to the alloy composition. The sequential separation and determination of osmium and platinum is reported.