INVESTIGATION OF METAL SULFIDE COMPLEXES IN SEA-WATER USING CATHODIC STRIPPING SQUARE-WAVE VOLTAMMETRY

Cathodic stripping square wave voltammetry has been used to detect H,S in sea water over a wide range of concentrations (nM to mM). The addition of metal ions to the solutions was found to depress the signal. This depression was attributed to the formation of metal sulfide complexes [MHS(+), M(HS),]. Stability constants for the formation of sulfide complexes with Cd2+, CU2+, Cu+, Pb2+, Zn2+, Co2+, Fe2+, Mn2+, Ni2+, Hg2+ have been estimated in sea water at pH 8.0 and 25 degrees C using this method. The stability constants of cadmium sulfide complexes (log beta(CdHS)=6.3 and log beta(Cd(HS)2)=12.7) were found to be in reasonable agreement with previous measurements. The values of log beta(CuHS)=7.0 and log beta(Cu(HS)2)=13.0; log beta(PbHS)=7.1 and log (Pb(HS)2)=13.5; log beta(ZnHS)=6.0 and log beta(Zn(HS)2)=13.7, log beta(FeHS)=log beta(CoHS)=log beta(NiHS)=5.3 and log beta(MnHS)=6.7 were also obtained. Correction for the formation of strong chloro complexes for Hg2+ and Cu+ in sea water gave measured values close to the literature values. The results have been used to determine the speciation of HS- in surface sea water and of a number of metal ions in various anoxic basins.