Identification of potential indicators of time-dependent tequila maturation and their determination by selected ion monitoring gas chromatography–mass spectrometry, using salting-out liquid–liquid extraction

Abstract

In this work, gas chromatography–mass spectrometry (GC–MS) profiles obtained for a series of rested and aged tequilas were statistically compared to identify volatile compounds indicative of time-dependent tequila maturation. For the determination of nine selected compounds, 2-acetylthiazole was added as internal standard, ethyl acetate extraction was carried out in the presence of sodium chloride (salting-out) and sodium sulfate was used to eliminate water traces. Baseline separation was achieved within 18 min and quantification was carried out by selected ion monitoring. The method detection limits were as follows: 2.10 µg L− 1 guaiacol (m/z 109), 1.78 µg L− 1 4-methylguaiacol (m/z 123), 1.97 µg L− 1 4-ethylguaiacol (m/z 137), 3.78 µg L− 1trans-whiskey lactone (m/z 99), 4.42 µg L− 1cis-whiskey lactone (m/z 99), 10.3 µg L− 1eugenol (m/z 103), 8.27 µg L− 1 vanillin (m/z 151), 14.2 µg L− 1 apocynin (m/z 151), 12.1 µg L− 1 syringaldehyde (m/z 182). For accuracy testing, 100 µg L− 1 of each analyte was added to silver tequila, yielding the recoveries in the range 92.1–116%. Data obtained in the analysis of 28 tequilas confirmed that the concentrations of individual compounds were changing among liquors at different maturation stage; however, due to many variables affecting the profile of volatile/semi-volatile compounds during aging in wooden barrels, discrimination of tequilas was not feasible. Otherwise, the proposed procedure allows for reliable determination of nine odor-active compounds in tequila at trace levels with simple sample pretreatment and short analytical run.