Simultaneous semi-automatic catalytic titration of binary mixtures of mercury(II) with copper(II) or cadmium at the micromolar level

Abstract Copper(II) and mercury(II) act as catalyst and inhibitor, respectively, for the oxidation of 4,4'-dihydroxybenzophenone thiosemicarbazone by hydrogen peroxide in an ammonium chloride medium. The combination of these two effects and blocking of the catalytic cycle by EDTA are used as the basis for titrimetric methods for individual and simultaneous titrations of mercury and copper or cadmium, with catalytic end-point detection. Mixtures can be resolved in the mole ratio range 20.1–4.1 for Cu/Hg and 27.1–1.1 for Cd/Hg. Titrations are viable for 10 −7 −10 −6 M mercury(II) and 10 −6 -10 −5 M copper(II) or cadmium(II).