Simultaneous determination of sulfite and phosphate in wine by means of immobilized enzyme reactions and amperometric detection in a flow-injection system

A flow-injection system is proposed for the simultaneous determination of sulfite and phosphate in wine. A sulfite oxidase immobilized reactor and purine nucleoside phosphorylase-xanthine oxidase co-immobilized reactor are incorporated at fixed positions (parallel configuration) in the flow line, which is based on the splitting of the flow after sample injection and subsequent confluence. A poly(1,2-diaminobenzene)-coated platinum electrode is used as an amperometric detector to detect selectively hydrogen peroxide generated enzymatically in the enzyme reactors, without any interference from oxidizable species and proteins present in wine. Because each channel has a different residence time, two peaks are obtained. The first peak corresponds to sulfite and the second peak to phosphate. The peak current is linearly related to the concentrations of sulfite between 1 × 10⁻⁵ and 2 × 10⁻³M and phosphate between 2 × 10⁻⁵ and 5 × 10⁻³M. The simultaneous determination of sulfite and phosphate in wine can be performed at a rate of 30 samples/hr with satisfactory precision (less than 1.2% RSD) and no pretreatment except for the sample dilution.