Gas-phase molecular absorption spectrometry: Determination of sulphite with diode-array detection

A method is described for determining sulphite by SO2 generation and UV-visible molecular absorption spectrometry with diode-array detection. The molecular absorption maximum of SO2 appears at 198 nm. The parameters affecting generation (particularly those relating to the kinetics of the process) and determination are optimized; under the optimum conditions found, only a 30 s preconcentration time is necessary. The linear response range is between 10 and 1000 μg ml−1 of SO32−, the RSD is 3.5% and the detection limit is 3.2 μg ml−1. The effect of different species on the SO2 signal is also studied. The method is applied to the determination of SO2 in air samples.