Determination of elemental sulphur, sulphide and their mixtures in electrolyte solutions by a.c. voltammetry

Abstract

The electrochemical behaviour of elemental sulphur, sulphide and their mixtures on a mercury electrode in 0.5 mol dm −3 NaCl-NaOH supporting electrolyte at pH 10 with and without the addition of 10% (v/v) methanol and 1 × 10 −5 mol dm −3 toluene was studied. Investigations were carried out over a wide concentration range (from 1 × 10 −8 to 1 × 10 −3 mol dm −3) of sulphur species in solution by a.c. voltammetry. Differences in the electrochemical behaviour during the formation of HgS at the electrode surface were observed between the two investigated species under different experimental conditions such as accumulation at different potential and voltammetric scan directions. Based on these differences, a method for the determination of sulphide, elemental sulphur and their mixtures in the aqueous solution is proposed. The solubility of elemental sulphur in aqueous medium at room temperature was determined as 1.7 × 10 −6 mol dm −3. The usefulness of the proposed method for the direct determination of sulphide and elemental sulphur in natural waters is discussed.