Rapid method for resveratrol determination by HPLC with electrochemical and UV detections in wines

The study describes an improved version of the reverse-phase-HPLC method. To determine free resveratrol isomers, the method uses isocratic elution and electrochemical detection with the use of a glassy working electrode at a potential of 0.75 V. The effects of important factors - Such as the isomerization of standard resveratrol solution in diffused daylight and its dependence on temperature or resveratrol isomerization in wine samples - were investigated. The equilibrium between trans- and cis-isomer was achieved after a 5-h exposure to the daily diffused light and it was not significantly influenced by the temperature (30-60 degreesC). Linearity was obtained in the concentration range from 0.01 to 10 mgl(-1). The detection limit (S/N = 3) was 3 mugl(-1) for trans-resveratrol and 15 mugl(-1) for cis-resveratrol. The trans- and cis-resveratrol were determined in selected Czech red and white wines and in the extract from Vitis vinifera plant. The concentration of trans-resveratrol ranged from 0.7 to 11 mgl(-1), that of cis-resveratrol from 0.6 to 5.1 mgl(-1). (C) 2004 Elsevier Ltd. All rights reserved.