In situ determination of sulfide profiles in sediment porewaters with a miniaturized Ag/Ag 2S electrode

Abstract

The use of silver containing epoxy resin allows the manufacturing of sulfide electrodes in arbitrary geometry and size. Electroplating with Ag provides a mirror-like surface essential for optimal performance. Miniature sensors were constructed using disposable pipette tips with 0.6 mm outer diameter. The reproducibility was ±0.11 % ( n = 9) and the response time ( τ 90) was 3–5 s. Selectivities for interfering anions were extremely high, and no interference by HS − was observed. The detection limit was determined with a continuous flow gradient dilution system and was found to be around 10 −20 moles S 2− l −1. The sensor was applied to the in situ measurements of sulfide concentration gradients at the sediment–water interface of a highly eutrophic lake. Concentration profiles from below the detection limit up to several micromoles were recorded within a layer of 2 mm. The flux of S(-II) from the sediment to the adjacent water was 0.5 × 10 −4 to 1.0 × 10 −4 moles (S-II) m −2 per day in winter when oxygen was mixed down to the sediment surface, and 1.8 × 10 −2 (S-II) m −2 per day in summer when the bottom water was devoid of oxygen.