Indirect complexometric titration of barium and strontium after stepwise precipitation as sulphate from homogeneous solution

Abstract

An indirect method has been developed for the stepwise titration of barium and strontium with EDTA, based on precipitation of the elements as sulphate from a homogeneous solution. Barium, strontium and other multivalent cations are complexed by titration with EDTA at pH 10·0 by using a mixed indicator comprising Eriochrome black T, Titan yellow and Naphthol green B. Barium is then selectively replaced from its EDTA complex and precipitated as the sulphate with an excess of magnesium sulphate solution. The excess of magnesium is determined by titration with EDTA and the equivalent concentration of barium is calculated. Strontium is determined in the same solution in the same way, with an excess of zinc sulphate solution.

The optimum conditions for precipitation and the interferences due to various anions and cations have also been studied. Copper, nickel, cobalt and iron interfere and a second method for the determination of barium alone has been derived wherein the interfering elements are complexed with triethanolamine, potassium cyanide and ascorbic acid. Phosphate and chromate interfere and require to be separated.