Enthalpimetric determination of sulphide and thiosulphate by the catalysis of the iodine-azide reaction

The enthalpimetric determination of sulphide and thiosulphate, in the presence and absence of Zn²⁺ and Cd²⁺, making use of the catalysis of the iodine-azide reaction is studied. An excess of the cations avoids losses of sulphide as H₂S and, when cadmium is used, a 30% enhancement of the sensitivity is observed in the determination of sulphide. On the other hand, both cations depress the analytical response produced by thiosulphate, but iodide can be used as an enhancement agent. Limits of detection of 0.1 and 0.3 ppm are obtained for sulphide and thiosulphate, respectively, and linear dynamic ranges comprise about two orders of magnitude.