Pervaporation flow injection analysis for the determination of sulphite in food samples utilising potassium permanganate–rhodamine B chemiluminescence detection

A simple pervaporation flow injection chemiluminescence (PFI-CL) procedure was utilised as an on-line separation for the analysis of contaminated sulphite in food samples. The method involves the injection of standard and/or sulphite sample solutions into a 0.20 M sulphuric acid donor stream. Sulphite is converted to sulphur dioxide and transported to the donor chamber of a pervaporation module. The sulphur dioxide gas then evaporates into the headspace and diffuses across a semi-permeable PTFE membrane into an acceptor stream containing 0.75% (m/v) sodium hexametaphosphate and 1.0 mg L−1 rhodamine B in 0.02 M H3PO4, which functions as a carrier solution for the chemiluminescence detection. The sulphur dioxide in the acceptor stream merges at a T-piece with a reagent stream consisting of potassium permanganate (8.0 × 10−5 M) prepared in the acidic sodium hexametaphosphate carrier solution. The elicited chemiluminescence intensity of the resulting reaction mixture was measured at a red sensitive photomultiplier tube operated at a voltage of 1.00 kV. Optimal experimental conditions for an on-line determination of sulphite were investigated. The second-order polynomial calibration curve was developed over the concentration range of 0.5–10.0 mg L−1 sulphite with a resulting equation of I = −0.239C2 + 4.846C − 1.64, r2 = 0.9997. The detection limit was found to be 0.2 mg L−1 with a sampling frequency of 30 h−1. The effects of common anionic and cationic interferences were also investigated. The proposed PFI procedure was successfully applied to the determination of sulphite in different food samples. The PFI data was validated versus standard differential pulse polarography.