Sequential injection system for the spectrophotometric determination of reducing sugars in wines

A sequential injection system for the spectrophotometric determination of r educing sugars in wines is described. The methodology is based on the forma tion of a coloured complex produced by the reaction of copper (I) with 2,9- dimethyl-1,10-phenanthroline (neocuproine), after reduction of copper (II) to copper (I) by reducing sugars. In the present SI system, a dialysis unit was incorporated not only to allow the sample dilution, but also to minimi se the interference of some coloured compounds. In this way, direct sample introduction into the system was possible, without any previous treatment o f the wine samples. The proposed method can be applied to the determination of reducing sugars in two concentration ranges: from 2 to 25 g l(-1) (tabl e wines) and from 20 to 140 g l(-1) (Port wines). To perform determinations in these two ranges, the manifold configuration remained the same; just a few operational parameters were changed in the controlling software. A samp ling-rate of 14-18 samples per hour was obtained with good repeatability fo r ten consecutive injections of wine samples (relative standard deviations (RSD) <2.1%). The results obtained from 19 wine samples were comparable to those obtained by the reference method. (C) 2000 Elsevier Science B.V. All rights reserved.