Spectrophotometric Determination of Sulfide in the Presence of Sulfite and Thiosulfate via the Precipitation of Bismuth(III) Sulfide

A photometric method has been developed for the determination of sulfide at 10-5 mol dm-3 levels, which is based on the reaction of sulfide with a given excess amount of bismuth(III) to form a precipitate of bismuth(III) sulfide and on the spectrophotometric measurement of the residual bismuth(III) at 335 nm after extracting with bismuthiol II reagent from an aqueous solution containing acetate buffer into benzene. The presence of sulfite and thiosulfate up to 0.002 mol dm-3 did not cause any interference in the determination of sulfide, because both sulfite and thiosulfate do not produce any precipitate with bismuth(III). A linear calibration plot with a negative slope was obtained for sulfide over the range of 5.00 x 10-7 - 3.00 x 10-5 mol dm-3 (16.0 - 960 ppb). An experimental calibration plot was in accord with the theoretical plot, taking into account the known excess of bismuth(III), showing that the reaction of sulfide with bismuth(III) proceeded to completion. The relative standard deviation of results from 10 replicate determinations of standard sulfide (2.00 x 10-5 mol dm-3) was 0.44%. The proposed method was successfully applied to the determination of sulfide in hot-spring water samples without any pretreatment.