Determination of anthocyanins in wine based on flow-injection, liquid--solid extraction, continuous evaporation and high-performance liquid chromatography--photometric detection.

A continuous method, easy to automate, for the determination of anthocyanins in wine based on the coupling of continuous liquid-solid extraction, evaporation, HPLC individual separation and photometric detection is proposed. The target analytes are removed from the wine in a continuous fashion using a C18 minicolumn and eluted with an aqueous solution (pH 2) with 16% acetonitrile. The eluted fraction is concentrated by solvent evaporation assisted by heat and dragging off the vapour using a flow of N2. For in-line preconcentration, a continuous evaporation module was designed and located in the manifold between the solid-phase minicolumn and the injection valve of the chromatograph. In this way, injection of the sample into the dynamic system leads the plug through it for liquid-solid extraction of the anthocyanins, partial evaporation of the eluent (with a preconcentration factor as required) and transport to the high-pressure injection valve of the chromatograph, where individual separation and subsequent photometric detection take place. The method thus developed for the determination of malvidin-3-glucoside, cyanidin-3-glucoside and peonidin-3-glucoside anthocyanins in Spanish red wines is more sensitive than the batch manual method based on the same steps, has better linearity of the calibrations curves with lower detection limits and much wider determination range for the most abundant anthocyanins in wine. In addition, the method can be fully automated with low acquisition and maintenance costs.