New reagent for indirect spectrophotometric red-ox determination of osmium (VI) Zholt Kormosh * , Svitlana Korolchuk Department of Analytical Chemistry, Volyn National University, 43021 Lutsk, Ukraine Abstract A highly sensitive indirect spectrophotometric red-ox method for the determination of osmium is reported. The method is based on the oxidation of iodide by osmium (VI) and the spectrophotometric detection of the liberated iodine in the form of complex anion and ion associate with 2-(4-diethylaminostyryl)-1,3,3-trimethyl-6-nitro-3H-indolium chloride reagent. The appropriate reaction conditions have been established. The molar absorptivity is (1.6–5.6)  10 4 L mol 1 cm 1 . Beer’s law holds for the concentration range of 0.5–11.4 mg mL 1 of Os(VI). # 2008 Zholt Kormosh. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Osmium; Determination; Spectrophotometry The accurate determination of platinum group metals in various matrices is one the most difficult analytical problems. Large variety and complexity of examined materials, inhomogeneous distribution of metals in the examined samples and wide range of concentrations to be determined make the selection of the analytical procedure a fundamental problem. Direct use of instrumental techniques for the determination of noble metals is considerably by owing to numerous interferences caused by various types of matrices [1–3]. UV–vis spectrophotometry was historically the first instrumental technique used for the quantification of small amounts of noble metals in various materials. The technique requires a quantitative conversion of the analytes into stable complexes that can act as the basis of spectrophotometric measurements [4]. The goal of this work was to investigate the new polymethine dye, 2-(4-diethylaminostyryl)-1,3,3-trimethyl-6- nitro-3H-indolium chloride (DENST), for the spectrophotometric red-ox determination of osmium (VI). www.elsevier.com/locate/cclet Available online at www.sciencedirect.com Chinese Chemical Letters 19 (2008) 716–719 * Corresponding author. E-mail address: kormosh@univer.lutsk.ua (Z. Kormosh). 1001-8417/$ – see front matter # 2008 Zholt Kormosh. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.04.026