Determination of sulfide by square-wave polarography

The application of square-wave polarography (SWP) to the determination of sulfide in water is reported. In comparison with other pulse techniques, cathodic stripping SWP was found to be the most sensitive. The details of the deposition and reduction of HgS were explored. The mechanisms of such deposition and reduction were found to be strongly dependent on the sulfide concentration but, in the observed analytical range, the HgS reduction process occurs close to the reversible potential. The influence of pH on the peak potential and on the peak current was studied; the results obtained are compared with those expected for a reversible process. The optimized analytical procedure allows the determination of sulfide in the 20–830 nM analytical range with a rate of 15 samples per h (calibration curve) or 10 samples per h (standard addition method). Thiosulfate and sulfite, but not sulfate, were found to interfere.