3.4.1. Determination of Volatile Phenols

The concentrations of VPs (guaiacol, 4-methylguaiacol, phenol, o-, m- and p-cresol, syringol and 4-methylsyringol) were measured in grape homogenate and wine (three replicates each), using gas chromatography–mass spectrometry (GC-MS) and stable isotope dilution analysis (SIDA) methods described previously [41,67]. These publications describe the preparation of isotopically labeled standards (d₄-guaiacol and d₃-syringol for analysis of grape juices performed at the University of Adelaide and d₃-guaiacol, d₃-4-methylguaiacol, d₇-o-cresol and d₃-syringol for analysis of wine performed by the Australian Wine Research Institute’s (AWRI) Commercial Services Laboratory), as well as method validation and instrumental operating conditions. All measurements were performed using an Agilent 6890 gas chromatograph coupled to a 5973 mass spectrometer (Agilent Technologies, Forest Hill, Vic., Australia). The limit of quantitation for VPs was 1–2 µg/L.