A spectrophotometric method for quantification of sulphite ions in environmental samples

This study described an alternative method developed for the quantification of sulphite ions in environmental samples. The method was based on results of an investigation of the reaction of excess pentacyanidonitrosylferrate(II) popularly known as nitroprusside (NP) and the sulphite anion. NP-SO32- reaction product by use of zinc-ethylenediamine complex cation(s) was stabilized. The NP-SO32-  reaction product was stabilized for 30 minutes by use of zinc ethylenediamine complex cation(s) and the absorbance was enhanced, making determination of sulphite possible. The method has a limit of quantification of 2.321 μg SO32- mL-1. Good accuracy was achieved for samples spiked with SO32- in the range from 1 to 10 µg SO32- mL-1, which demonstrated the validity of the proposed procedure. The repeatability (CV) was not more than 2.37% and the limit of detection was estimated at 0.99 μg SO32- mL-1. The method was applied to determine the concentration of sulphite ions in sugar and wine brands sold in local market. Comparable results were obtained between this method and an iodometric procedure for determination of sulphite in environmental samples.   Key words: Determination of sulphite ions, wine, sugar, environmental samples.