Two-parameter determination in vinegar by a flow injection-pervaporation system

A flow injection method (FI) for the sequential determination of ethanol and acetic acid in vinegar is reported. The determination of ethanol is based on the oxidation of the pervaporated ethanol by K2Cr2O7. The acetic acid is determined by an acid-base reaction with Thymol Blue as the indicator. Both reactions are monitored photometrically at 600 nm using a single detector. Optimisation studies and assessment of the sequential FI method are also reported. The linear determination range is 0-12% v/v for ethanol and 0-10% (grams of acetic acid in 100 ml) for acetic acid. The sample throughput of the sequential manifold is seven per hour. The new method was applied to vinegar samples and the results obtained were in excellent agreement with those from reference methods used in Spain.