Sequential determination of total and volatile acidity in wines based on a flow injection-pervaporation approach

A method for the sequential determination of the total and volatile acidity in wines based on the use of a pervaporator inserted in a continuous manifold is reported. The chemical principle is the colour change of bromothymol blue in the presence of the analytes and monitoring of the absorbance at 616 nm. The simultaneous injection of two sample aliquots into two channels allows one of the plugs to be driven to the pervaporator and the other directly to the photometric detector after merging with an indicator stream. After pervaporation, the acceptor stream, also containing the indicator, is led to the photometric detector for monitoring. The detection limits and relative standard deviation are 10 meg l(-1), 1.0%, and 0.02 g l(-1), 5.0%, for total and volatile acidity, respectively. The method has been applied to white and red wines from different origins and the results obtained an in good agreement with those of the standard method used in Spanish wine industries. (C) 1999 Elsevier Science B.V. All rights reserved.