Development of a new stir bar sorptive extraction method for the determination of medium-level volatile thiols in wine.

A fast, simple, and reliable analytical method for the determination of medium-level volatile thiols in wines is presented. Stir bar sorptive extraction using ethylene glycol-silicone coated stir bars has been used in combination with thermal desorption gas chromatography with mass spectrometry for the analysis of 4-mercapto-4-methylpentan-2-one, 2-furanmethanethiol, 3-mercaptohexyl acetate, and 3-mercaptohexanol in wine. Optimization of the extraction technique was performed using a two-level fractional factorial design. For the extraction step, the optimum conditions were: Ethylene glycol and silicone coated stir bars, pH at 3.5, sample volume of 25 mL, extraction time of 90 min, NaCl content 4.0 g, and stirring speed at 500 rpm. The optimized method achieved good linearity for all studied compounds (r(2) > 0.995) and it provided detection limits of 21.52, 0.36, 0.73, and 2.55 μg/L for 4-mercapto-4-methylpentan-2-one, 2-furanmethanethiol, 3-mercaptohexyl acetate, and 3-mercaptohexanol, respectively. It was repeatable, with precisions lower than 18% relative standard deviation for both intraday and interday repeatability. The developed procedure is suitable for the determination of these kinds of compounds when they are present at medium concentration levels. It was finally applied to real wine samples with negative aroma derived from the high concentration levels of these compounds.