Simultaneous determination of ethanol and glycerol in wines by a flow injection-pervaporation approach with in parallel photometric and fluorimetric detection

A simultaneous method for the determination of ethanol and glycerol in wines based on the coupling of pervaporation-chemical derivatisation-photometric detection for ethanol and biochemical derivatisation-fluorimetric detection for glycerol is proposed. After separation by pervaporation the ethanol is collected in a K2Cr2O7 acceptor stream and the Cr3+ formed is driven to the spectrophotometer and monitored at 600 nm. The determination of glycerol is based on its oxidation by oxidised beta-nicotinamide adenine dinucleotide (beta-NAD(+)) catalysed by glycerol dehydrogenase immobilised on controlled-pore glass, the reduced form of the coenzyme (NADH) being spectrofluorimetrically monitored (lambda(ex) = 340 nm, lambda(em) = 460 nm). The linear determination range is between 1-20% for ethanol and 2-8 g l(-1) for glycerol, with RSDs 3 and 2%, respectively. The method applied to red and white Spanish wines, compares well with the official methods for these analytes. (C) 2000 Elsevier Science B.V. All rights reserved.