Flow injection determination of sulfite in wines and fruit juices by using a bulk acoustic wave impedance sensor coupled to a membrane separation technique

A flow injection analysis (FIA) method was developed for the rapid determination of sulfite in wines and fruit juices. The method is based on an on-line membrane separation of the SO2 released from a stream of 0.5 M H2SO4 into a stream of 0.01 M H2O2–0.15 mM H2SO4. The conductance increase due to the oxidation of SO2 to H2SO4 is monitored by a bulk acoustic wave impedance sensor and the signal is proportional to the concentration of sulfite present in the original sample. At a throughput of 78 samples h–1, the method exhibited a linear frequency response up to 1.0 mM sulfite with a detection limit of 5.0 µM, and the relative standard deviation of the peak height (n = 6) ranged from 0.57 to 1.23%. Results obtained by the proposed method agreed well with those obtained by conventional iodimetry. The effects of several factors, including those affecting the detector performance and gas transfer process, on the performance of the proposed FIA system were also examined.