Detecting and resolving the low concentration species associated with beer aroma analysis relies on the high speed and sensitivity of the Vocus PTR-TOF.
Luca Cappellin1, Felipe Lopez-Hilfiker1, Megan Claflin2
1. TOFWERK, Thun, Switzerland 2. Aerodyne Research, Billerica, MA, USA
Terpenes and other aroma compounds determine the unique flavors that affect consumers’ wine and beer preferences. Proton transfer reaction mass spectrometry (PTR-MS) is a fast and sensitive method for the analysis of volatile organic compounds (VOCs), including these beer aroma compounds. However, the analysis of alcoholic beverages by PTR-MS is challenging because the high-concentration of ethanol titrates the instrument, preventing the accurate measurement of lower concentration VOCs that are present in the liquid or headspace. Moreover PTR-MS cannot distinguish between isomers, such as different monoterpenes or sesquiterpenes, which have the same elemental composition but different molecular structures.
Quantification of Low Concentration Beer Aroma VOC Isomers
To quantify low concentration VOC isomers, a fast gas chromatogram (GC) – which can separate isomers – was coupled in line with a TOFWERK Vocus 2R PTR-TOF. As ethanol elutes from the GC well before most aroma compounds, quantitative flavor analysis of alcoholic beverages becomes possible.
Figure 1 demonstrates analysis of beer headspace with the Vocus GC-PTR-TOF. Mass spectral peaks at mass/charge 137.1325 Th and 205.1951 Th were determined to be monoterpenes and sesquiterpenes, respectively, by exact mass analysis.
Figure 2 shows an example this analysis, whereby the TOF resolves terpenes from co-eluting VOCs having similar mass/charge. The numerous chromatographic peaks observed at each of these mass/charge values in Figure 1 are isomeric monoterpenes (red) and sesquiterpenes (blue).
Several isomers of each compound class are baseline separated allowing easy quantification. Detecting and resolving these low concentration species with fast GC relies on the high speed (10 mass spectra per second) and sensitivity (10000 cps/ppbv) of the Vocus PTR-TOF.