Spectrofluorimetric determination of sulphide in natural and wastewaters with 1,2-naphthoquinone-4-sulphonate

Abstract

A simple and sensitive spectrofluorimetric method for the determination of sulphide with 1,2-naphthoquinone-4-sulphonate (NS) has been developed. Sulphide in water samples (preserved as ZnS and then dissolved at pH 5.2 with ethylenediaminetetraacetic acid) gives a blue fluorescence (λ_ex 235 nm and λ_em 470 nm) after reaction with NS, which allows the quantitative determination of this species. The samples were stored in the dark by wrapping the storage flasks in aluminium foil. Sulphide can be determined in solutions with concentrations in the range 0.08–0.48 µg ml^–1 with a coefficient of variation of 3.20%(p= 0.10; n= 15) for a concentration of 0.25 µg ml^–1. The proposed method is tolerant of many common cations and anions. A 280-fold excess of cyanide with respect to sulphide does not interfere with the analysis. A complementary procedure including a prior distillation step is described for samples with suspended materials or with a lower sulphide content. To test the utility of both procedures (direct and with distillation) various samples of natural waters, industrial wastewaters and municipal wastewaters were successfully analysed.