Gas diffusion and micellar catalysis in the flow injection determination of sulfite

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Abstract
A flow injection method for the determination of sulfite using gas diffusion and micellar catalysis has been developed. The analyte was detected by reaction with 5,5′-dithiobis(2-nitrobenzoic acid)(DTNB) in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). Use of a prior separation process affords an improvement in selectivity and the location of the diffusion unit in the loop of the injection valve enables enrichment of the acceptor leading to better sensitivity. The micellar catalysis of the derivatization reaction involves faster kinetics with improved sensitivity. Furthermore, the shift in the optimum reaction pH leads to a lower noise level and improved detection limits. The proposed method has been applied to the determination of free and combined sulfite in samples of wine and shrimp. The sensitivity attained with the proposed procedure permits high dilution factors for the samples, thus minimizing the matrix effects