A multi-purpose flow manifold for the spectrophotometric determination of sulphide, sulphite and ethanol involving gas diffusion: application to wine and molasses analysis.

A simple and rugged flow set up was designed for spectrophotometric determination of sulphide, sulphite and ethanol aiming at quality assessment of wines, control of industrial fermentation, and selection of yeast strain. The different assays involved gas diffusion through a Teflon planar membrane and were carried out after minor modifications in the manifold, namely reagent composition and total flow rate. Main figures of merit: linear analytical curves=0.50-6.0 mg L(-1)S(2-), 2.5-20.0 mg L(-1) SO3(-) and 5.0-25.0% (v/v) of ethanol; detection limits (3σ)=0.035 mg L(-1)S(2-), 0.2 mg L(-1) SO3(-) and 0.18% (v/v) of ethanol; peak height r.s.d.=2.18% for 4.03 mg L(-1)S(2-) spiked molasses, 2.21% for a 9.82 mg L(-1) SO3(-) wine and 2.07% for a typical wine (12.53% v/v of ethanol), sampling rate=15, 57 and 29 h(-1), reagent consumptions=1.9 µmol of N,N-dimethyl-p-phenylenediamine, 1.68 µg of Malachite green and 0.68 mmol Cr(VI) per determination, respectively.