Methanol concentration as a preceding eliminative marker for the authentication of Scotch Whiskies in Taiwan

Modern rectified spirit is distilled ethanol (EtOH) containing only a tiny amount of methanol (MeOH), as opposed to former industrial alcohol, and is frequently used by perpetrators to adulterate or counterfeit Scotch whiskies in Taiwan. As a result, MeOH level presents an obvious discrepancy between adulterated whiskies and authentic Scotch whiskies. In this study, 54 authentic single malt Scotch whisky samples and 30 authentic blended Scotch whisky samples were comparatively analyzed. Instead of various analog internal standards often spiked for GC/MS quantitative analyses, the isotope-labeled internal standard ²H₃-MeOH was employed for optimizing the Scotch whisky analysis to achieve a limit of quantitation (LOQ) of 5 ppm for MeOH. The resulting data were further analyzed by a distribution fitting method and showed that the distribution of MeOH levels corresponded to a lognormal distribution for both authentic single malt Scotch whiskies and authentic blended Scotch whiskies. Based on the statistical characteristics of the lognormal distribution, 99.7% of the MeOH concentrations would lie between 13.4 and 44.2 ppm for authentic single malt Scotch whiskies and between 7.87 and 74.9 ppm for authentic blended Scotch whiskies, suggesting that the MeOH level might serve as a marker for the authentication of the seized Scotch whiskies in Taiwan.