Stir bar sorptive extraction with gas chromatography–mass spectrometry for the determination of resveratrol, piceatannol and oxyresveratrol isomers in wines

• cis/trans-Isomers of resveratrol, piceatannol and oxyresveratrol are determined by SBSE-GC–MS.
• A new and easy to perform way to obtain the cis-isomers is given.
• Analysis of wine samples is carried out using aqueous standards for calibration.

A simple and highly sensitive procedure based on stir bar sorptive extraction coupled to gas chromatography–mass spectrometry by means of a thermal desorption unit (SBSE-TD-GC–MS) has been optimized for the determination of cis/trans isomers of resveratrol, piceatannol and oxyresveratrol in wine samples. Quantification of the cis-isomers was carried out by generating the standards from the corresponding trans-species once they had been preconcentrated on the SBSE extracting phase. The optimization of the acetylation derivatization, SBSE extraction and thermal desorption steps was investigated using Plackett–Burman designs, taking into account the high number of variables to be considered. The use of bisphenol F as internal standard allowed quantification of the samples against aqueous standards. Repeatability, expressed as relative standard deviation of 10 successive analyses was between 5% and 9%, confirming the high precision attained under the optimized conditions. Satisfactory recovery values of between 79% and 109% were obtained for spiked samples in the 0.2–1.0 μg L−1 concentration range, depending on the compound. The main compound determined in the analyzed samples was trans-resveratrol, with concentrations in the range of 3–230 μg L−1, depending on the type of wine.