Determination of trace-levels of sulfide by high-sensitivity potentiometry with a carbon paste electrode

Abstract

A new potentiometric method for determining sulfide is investigated. In 0.0787 mol l^–1 sodium tetraborate buffer (pH = 9.00), a carbon paste electrode is used to determine sulfide at a trace level (20 °C). When the sulfide concentration is within a range of 1.5 × 10^–7–2.5 × 10^–6 mol l^–1, the linear response slope of the electrode is 130–180 mV decade^–1, whereas when the concentration is 7.0 × 10^–6–1 × 10^–3 mol l^–1 the linear response slope is 40–60 mV decade^–1, the detection limit being 5 × 10^–8 mol l^–1. In determining trace levels of sulfide, 1000 times the concentration of cyanide, Br^–, I^–, thiosulfate, sulfite and phosphate do not interfere. This method, when applied to the determination of sulfide in waste water, is characterized by convenience, low cost and speed. The potential response behaviour is caused chiefly by chemisorption of sulfide to the surface of the carbon.