Chelatometric determination of cyanide, thiocyanate and chloride in presence of one another

Abstract

A chelatometric method for the determination of cyanide, thiocyanate and chloride in the presence of one another is described. In one portion of the sample all three ions are precipitated by adding silver nitrate in excess. The silver precipitates are boiled with concentrated nitric acid. Silver chloride is not affected by this treatment while silver cyanide and thiocyanate are decomposed. The latter is oxidised to sulphate, the cyanide being expelled. The silver chloride precipitate is dissolved in a solution of potassium tetracyanonickelate and the liberated nickel is titrated with EDTA, the chloride content thus being determined indirectly. The sulphate solution after oxidation of thiocyanate is treated with a known volume of barium chloride solution and the excess of barium is titrated with EDTA solution of the same molarity. The difference between the volumes of barium chloride and EDTA solutions multiplied by a factor gives the thiocyanate content of the sample. In a second portion of the sample, cyanide is determined by adding a known volume, in excess, of nickel sulphate solution and titrating the excess of nickel that has not combined with the cyanide. The difference between the volumes of the nickel and EDTA solutions multiplied by a factor gives the cyanide contents. The method is rapid and accurate. A very small quantity of one of the components in the presence of large amounts of the others can be determined.