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 °C). Linearity was obtained in the concentration range from 0.01 to 10 mg l−1. The detection limit (S/N=3) was 3 μg l−1 for trans-resveratrol and 15 μg l−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 mg l−1, that of cis-resveratrol from 0.6 to 5.1 mg l−1.