Sequential injection flow system with improved sample throughput: determination of glycerol and ethanol in wines

The performance of sequential injection (SI) systems has often been criticized for its low sampling frequency. The present work describes a SI system where an injection valve and an additional pump were incorporated to enhance sample throughput rate. The proposed system was applied to the enzymatic determination of glycerol and ethanol in wines, using spectrophotometric detection and immobilized glycerol and alcohol dehydrogenases. The method proposed was applied to the determination of ethanol between 0.10 and 0.50% (v/v) and glycerol between 0.03 and 0.30 g l⁻¹. These ranges were appropriate for determination in table and port wines, since samples were diluted 50 times before introduction into the system. The results obtained from 15 wine samples were statistically comparable to those obtained by the reference methods, with good repeatability (R.S.D.<3.4%, n=10). The sampling rate was 22.5 h⁻¹, corresponding to 45 determinations per hour. This way, the time required for each determination was decreased by 30% when compared to a conventional SI system.