Analysis of Hop-Derived Thiols in Beer Using On-Fiber Derivatization in Combination with HS-SPME and GC-MS/MS

The quantitation of the hop varietal thiols 4-mercapto-4-methyl-2-pentanone (4MMP), 3-mercapto-1-hexanol (3MH), and 3-mercaptohexylacetate (3MHA) from beer is challenging. This primarily relates to their low concentration (ng/L levels) and their reactivity. Published assays for thiol quantitation from beer include complex and/or time-consuming sample preparation procedures involving manual handling and use reagents that are harmful because they contain mercury. To facilitate thiol analysis from beer, the current article is concerned with the implementation of an automated headspace solid-phase microextraction (HS-SPME) on-fiber derivatization (OFD) approach using 2,3,4,5,6-pentafluorobenzyl bromide followed by gas chromatography-tandem mass spectrometry (GC-MS/MS). Optimization of HS-SPME and MRM conditions was based on a central composite design approach. The final OFD-HS-SPME-GC-MS/MS method yielded limits of quantitation below the sensory thresholds of 4MMP, 3MH, and 3MHA. Method validation and application on beers brewed with German, Australian, and US hops, as well as with added fruits displayed excellent method performance.