Kinetic- spectrophotometric determination of trace amounts of sulfide with malachite green in micellar medium

Abstract

The determination of trace amount of sulfide based on the addition reaction of sulfide with malachite green at pH= 7.5 and 25 oC has been investigated in micellar media. Surfactants studied include non-ionic surfactant, Trition-x-100, anionic surfactant, sodium dodecyl sulfate (SDS), cationic surfactant, cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC). The reaction is followed spectrophotometrically by measuring the decrease in absorbance of the indicator at l max = 630 nm by the fixed time method. The reaction in the presence of Trition-x-100 is faster than in the absence of surfactant in medium. No significant change was observed with SDS, CTAB and CPC. Under the optimum experimental conditions decreases in the absorbance of malachite green is proportional to the concentration of sulfide in the range 25-1750 ng.ml -1 with a fixed time method at the first 5, 15 and 25 seconds from initiation of the reaction. The detection limit and quantification limit of the proposed kinetic method were 0.166, 0.207and 0.281μgml -1 (Dt=5,15 and 25)and 0. 555, 0.692and 0.959μgml -1 (Dt=5,15and 25) respectively. To confirm the usefulness of the proposed method, sulfide was determined in river, spring, fish farm, and tap water wastewater samples without any purification or using masking reagents.