A spectrophotometric study of osmium (VIII) complex of 1-hydroxy 2- pyridine thione (HPT) is presented. A red-violet complex, Os (HPT)4 is formed in a highly ~cidic solution, and shows maximum absorbance at 500 nm with molar absorptivity of 5.12 x 101. mol1• cm·1• Beer s law is obeyed in the range of 3-60 ppm. Sandel s sensitivity of the method is 0.37 p,g. cm-2per0.001 absorbance unit. V (V), Pt (IV), Cu (II), Sn (IV), Cr (VI), and N03• interference. To overcome the interference and improve the selectivity, the Os (VIII) as OsO 4 is extracted in CCI4 and the extracted Os (VIII) is converted to the complex and measured spectrophotometrically. This method reduces the number of interferences to V(V), Pt (IV), and N03-. The method offers the advantages of simplicity, speed and high precision. A spot test for the detection of traces of osmium is also presented. Introduction Several methods have been proposed dealing with various chromogenic reagents for the determination of Jsmium (1-5]. A number of procedures are based on :he catalytic effect of osmium in a specific reaction [6, 7]. Some of these reagents react slowly with osmium and conditions for obtaining reproducible color are usually empirical. The sodium salt of !-hydroxy 2-pyridine thione was used for spectrophotometric determination of Fe (III), Pd and turbidimetric determination of Ag [8-10]. In this study, HPT is suggested as a reagent for spectrophotometric determination of osmium (VIII) and its detection by spot test. This reagent forms an intense red-violet coloration with Os (VIII). The complex shows an absorption maximum at 500 nm, which appears to be a sensitive reagent for the detemination of microgram amounts of osmium (VIII) with the advantages of simplicity, rapid determination in highly acidic solutions and reasonable selectivity.

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