Sensitized synchronous fluorimetric determination of trans-resveratrol and trans-piceid in red wine based on their immobilization on nylon membranes

It has been carried out the determination of trans-resveratrol and trans-piceid in red wine samples by using room temperature synchronous fluorescence, sensitized through their retention on nylon membranes, in front-face mode. These compounds are weakly fluorescent in solution but their retention allows using the native fluorescence of these compounds as analytical signal, due to the increase in the medium rigidity. To determine these compounds in red wine, a previous liquid-liquid extraction is necessary and in the case of trans-resveratrol it is also necessary a previous cleanup stage using C18 cartridges. Diethylether and ethyl acetate are the selected extractant solvents for trans-resvertarol and trans-piceid, respectively. The retention on nylon membranes was carried out by immersion of the membranes in solutions of these compounds. Variables involved in the retention and measurement processes were optimized, and the analytical figures of merit were obtained under optimal conditions. Ethanol:water 10:90 v:v and ethyl acetate were the solvents used for the retention of trans-resveratrol and trans-piceid, respectively and, for each case a immersion time of 300 and 600 s was selected. Satisfactory linear relation between fluorescence intensity and concentration was found in the intervals 0.040 and 0.242 mg L⁻¹ of trans-resvertarol and 0.009 and 0.288 mg L⁻¹ of trans-piceid. Concentration of 1.08 ± 0.21 mg L⁻¹ for trans-resveratrol and 1.49 ± 0.36 mg L⁻¹ for trans-piceid were found in a wine sample obtained from a pool of commercial red wines.