Sensitive spectrophotometric determination of osmium with tin(II) chloride and Rhodamine B after flotation using cyclohexane
Abstract
Spectrophotometric studies of the reaction of osmium with tin(II) chloride have been carried out. The optimum conditions [hydrochloric acid and tin(II) chloride concentrations and the time of heating] under which a stable, anionic complex of osmium, OsCl2(SnCl3)22–(λ= 385 nm, ε= 2.4 × 10–3 l mol–1 cm–1), is formed have been established. A sensitive method for the determination of microgram amounts of osmium, based on an ion associate with Rhodamine B (RB), has been developed. The ion associate is separated by flotation from 0.5 M HCl-2.5 × 10–4M RB-0.1 M SnCl2 with cyclohexane and dissolved in acetone, and its molar absorptivity is 4.1 × 105 l mol–1 cm–1 at 560 nm. The solutions of the complex obey Beer's law in the range 0.05–0.4 µg ml–1 of osmium. The relative standard deviation is 2–8%. The Os : RB molar ratio in the complex is 1 : 4, and its composition as the adduct [(RB+)2OsCl2(SnCl3)22–].2(RB+SnCl3–) has been established. Ruthenium reacts similarly. The determination of osmium is selective after its separation as OsO4 from nitric acid. The method has been applied to the determination of osmium in mixtures of platinum metals.