Determination of sulphide using flow injection analysis with a coated tubular solid-state silver sulphide ion-selective electrode

Abstract

The construction, characteristics and application of a laboratory-built coated tubular solid-state sulphide-selective electrode are described. Tygon tubing and silver foil are used to construct the tubular flow-through sensor. Treatment of the constructed tubular silver foil with a sodium sulphide solution yields an active membrane (volume, 15.7 µl). The active sensor is conditioned and stored in sodium sulphide solution. The effect of interferences is similar to that found in batch analysis, but is less severe with the compact tubular membrane and sample volumes of 30 µl used in the flow injection analysis (FIA) system. Among the advantages offered by the tubular membrane when evaluated against a commercial cascade mode electrode are higher sensitivity and less carry-over in FIA. The constructed tubular electrode covers a working range of up to 1000 mg dm^–3 with a detection limit of 0.4 mg dm^–3 when 30 µl samples are injected. The system is suitable for the determination of soluble sulphide in effluent water samples in the range 0.4–24 mg dm^–3 with a relative standard deviation of better than 1.8% at a sampling rate of 60 samples h^–1.