Voltammetric determination of elemental sulfur in pore waters
Limnol. Oceanogr., 43(6), 1998, 1353-1361 | DOI: 10.4319/lo.19188.8.131.523
ABSTRACT: We describe a new simple, reliable, and sensitive method that employs square-wave cathodic stripping voltammetry (SWCSV) for the measurement of dissolved elemental sulfur, S(0), in pore waters. The method, which requires only small pore-water samples (~1.5 ml), shows a linear relationship over three orders of magnitude (~10-9-10-6 Eq S liter-1) between peak current or peak area and S(0) concentration; the practical detection limit (3 X 10-9 Eq S liter-1) is below that required for most pore waters. Experiments carried out over a wide range of pH (2.5-11.5) indicate that peak current and peak potential vary with pH and that thiosulfate, sulfite, and thiols (and probably humic substances) would not interfere with the determination of S(0) over this pH range; interference from sulfide is easily removed by acidifying and bubbling with N2. The slopes (nA/Eq S liter-1) obtained by standard additions of S(0) to pore-water samples containing 10 mg liter-1 dissolved organic carbon were not statistically different from the slopes of calibration curves, indicating that fouling effects due to natural organic matter should be minimal. Porewater concentration profiles obtained at an anoxic site of a Shield lake indicate that S(0) concentrations were greater than those predicted from equilibrium with orthorhombic sulfur.