Simultaneous determination of ethanol and total sulfite in white wine using on-line cone reservoirs membraneless gas-liquid separation flow system

Abstract

This work presents the use of a single membraneless vaporization unit (MBL-VP unit) in a flow system for the simultaneous determination of ethanol and total sulfite in white wine. The flow system comprises a MBL-VP unit with three cone-shaped reservoirs and two in-house detectors, a paired emitter-detector diodes (PEDD) and a capacitively coupled contactless conductivity detector (C4D). The sample of white wine is first acidified in the flow system. Then 200-μL of the acidified sample is delivered to the donor reservoir of the MBL-VP unit in which the two acceptor reservoirs contain 200-μL of the gas acceptor reagents, viz. acidic permanganate solution and deionized water. Vaporization of ethanol and SO2(g) (converted from sulfite) from the donor into the acceptor reservoirs is carried out for 15 s. The two acceptor solutions are then simultaneously transferred for separate detection at the PEDD and C4D detectors. Decolorization of the permanganate solution by the reduction reaction with absorbed ethanol gives an increase in the PEDD signal, whereas dissolution of the SO2(g) in the water acceptor leads to an increase in conductivity and detected by the C4D. Linear calibrations were obtained in the range of 5.0–15.0% (v/v) for ethanol (PEDD signal = ((4.0 ± 0.03) × 10−2) · (%(v/v) ethanol) – ((1.85 ± 0.35) × 10−2): r2 = 0.999) and 10–200 mg L−1 for sulfite (C4D signal = ((0.64 ± 0.015) × 10−2) · (mg L−1 sulfite) – ((3.25 ± 1.64) × 10−2): r2 = 0.999). The analysis is rapid with total analysis time of 2.5 min. Percentage of recoveries were 81–104% and 88–110% for ethanol and sulfite, respectively. The method was compared with gas chromatographic analysis and iodometric titration for ethanol and sulfite, respectively, with no statistically significant difference for the analysis of seven white wine samples.