Spectrophotometric Determination of Micro Amounts of Thiocyanate via Permanganate Reaction

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Abstract
A method has been developed for the determination of micro amounts of thiocyanate. It is based on the reaction of thiocyanate with a given amount of permanganate as an oxidizing agent in a dilute sulfuric acid medium and on the spectrophotometric measurement of iodine as triiodide, which is formed by the oxidation of iodide with an excess of permanganate for its reaction with thiocyanate. The conditions for the thiocyanate to be quantitatively oxidized were established by varying the temperature, reaction time, and amounts of sulfuric acid and permanganate. The present method can be successfully applied to the determination of thiocyanate in the range from 7×10−7 to 4×10−5 mol dm−3 (0.4–23.2 μg SCN− in 10 cm3). In eleven determinations for 10-cm3 sample solutions containing 0.250 μmol of thiocyanate, the present method gave a mean value of 0.251 μmol, with a standard deviation of 0.0022 μmol and a relative standard deviation of 0.88%. Chloride, bromide, iodide, and cyanide did not interfere with the determination of 14.5 μg of thiocyanate in the presence of 1000 μg, 500 μg, 100 μg and 50 μg, respectively.