INDIRECT COMPLEXOMETRIC DETERMINATION OF MERCURY(II) USING SODIUM THIOSULFATE AS A MASKING REAGENT

A complexometric method for the determination of mercury in the presen ce of other metal ions based on the selective masking ability of thios ulfate toward mercury is described. Mercury (II) present in a given sa mple solution is first complexed with a known excess of EDTA and the s urplus EDTA is titrated against zinc sulfate solution at pH 5.0-6.0 (h examine) using xylenol orange/methylthymol blue complexone as indicato r. A known excess of sodium thiosulfate solution (1%) is then added, t he mixture is shaken well, and the EDTA released from the Hg-EDTA comp lex is titrated against a standard zinc sulfate solution. Reproducible and accurate results are obtained for 2.5-78 mg of mercury with relat ive errors <0.4% and standard deviations less than or equal to 0.05 mg . The interference of various ions were studied. This method was appli ed to the determination of mercury (II) in its alloy compositions. Aca demic Press, Inc. (C) 1996 Academic Press, Inc.