SELECTIVE COMPLEXOMETRIC DETERMINATION OF MERCURY USING SODIUM-NITRITE AS MASKING AGENT

A complexo-titrimetric method for the determination of mercury(II) in the presence of other metal ions is described based on the selective m asking ability of sodium nitrite. Mercury and other ions are initially complexed with an excess of EDTA and the surplus EDTA is titrated wit h Pb(NO3)(2) solution at pH 5.0-6.0 using xylenol orange as indicator. An excess of solid NaNO2 is then added to decompose the Hg(II)-EDTA c omplex and the released EDTA is titrated with standard Pb(NO3)(2) solu tion. Accurate results were obtained for 10-65 mg of mercury with rela tive errors < 0.3% and standard deviations < 0.03 mg. Sn(IV) and Pd(II ) interfere but can be easily masked. The method is applied for the de termination of Hg(II) in its alloy compositions and complexes.