Determination of hydroxylated stilbenes in wine by dispersive liquid-liquid microextraction followed by gas chromatography mass spectrometry.

Dispersive liquid-liquid microextraction (DLLME) has been proposed, for first time, to determine the concentrations of three hydroxylated stilbenes (trans-isomers of pterostilbene, resveratrol and piceatannol) in wine samples. DLLME was preceded by an acetylation step and followed by gas chromatography mass spectrometry (GC-MS) to achieve limits of quantification (LOQs) comprised between 0.6 and 5 ngmL(-1), linear responses up to 5000 ngmL(-1), excellent accuracy (overall recoveries ranged from 90 to 102% for samples spiked at different levels from 50 to 1000 ngmL(-1)) and standard deviations below 12%. Sample intake and organic solvents consumption remained at 1 and 0.6 mL, respectively, with a total sample preparation (derivatization and concentration) time around 15 min. The trans-isomers of piceatannol and resveratrol were measured in wine samples at concentrations up to 0.5 and 2.6 μgmL(-1), respectively. In addition to their cis-forms, the dihydrogenated analogues of both antioxidants were detected in red wines. To the best of our knowledge, this is the first report describing the presence of dihydropiceatannol in wine. On the other hand, pterostilbene remained below the detection limits of the method in all the processed samples. In addition to the relative low levels of this stilbene existing in grapes, its lipophilic character appears to limit the transfer from grapes skins to wine.