Exploiting Sulphide Generation and Gas Diffusion Separation in a Flow System for Indirect Sulphite Determination in Wines and Fruit Juices

A flow system for sulphite determination in wines and fruit juice samples has been developed exploiting H₂S generation and gas diffusion separation. The composed sandwich gas diffusion cell was coupled in the flow manifold to permit sulphite reduction to H₂S and H₂S diffusion through a microporous PTFE membrane to produce methylene blue resulting from the reaction with N,N-dimethylphenylene diamine (DMPD) and Fe³⁺. The flow parameters were optimized, and the best results were obtained by using NaOH solution for H₂S collection. Interferences of H₂S, CO₂ and ascorbic acid were evaluated. Limits of detection (3σ) for the free and total sulfite were calculated at 0.12 and 0.25 mg L⁻¹, respectively. The results obtained by the proposed process were in agreement with the reference methods for a 95% confidence level.