旁若无‘醇’,GC-PTR-MS:快速检测啤酒香味物质

Fast Analysis of Beer Aroma with GC-PTR-MS

啤酒中痕量香味物质的定性定量检测,取决于Vocus PTR-TOF的快速响应和高灵敏度。

Luca Cappellin1, Felipe Lopez-Hilfiker1, Megan Claflin2
1. TOFWERK, Thun, Switzerland 2. Aerodyne Research, Billerica, MA, USA

酒精类饮品(啤酒和红酒等)独特的味道源于其所含的萜烯和其他芳香化合物。目前,PTR-MS仪器因响应速度快、灵敏度高,广泛用来在线监测挥发性有机物(VOCs),当中也包含啤酒香味物质。然而,PTR-MS方法对酒精饮料中痕量挥发性有机物的检测仍存在一定的困难。一是酒精饮料中高浓度乙醇会让PTR-MS检测器响应超饱和,从而降低其他低浓度VOCs的测量精度。其次,PTR-MS对同分异构体的区分能力较低,如单松烯类和倍半萜烯。

定量分析啤酒中低浓度的同分异构香味物质

为定量分析痕量同分异构VOCs,在TOFWERK Vocus 2R PTR-TOF前端配置了一台快速气相色谱(fast GC),从而实现有效分离同分异构体。同时,乙醇在气相色谱中会先于其他待测物洗脱出来,从而实现对酒精饮料中香味物质的精确定量分析。

图1是Vocus GC-PTR-TOF对啤酒顶空气体中香味物质的分析结果,谱图中精确质量在137.1325 Th 和205.1951 Th的峰分别对应的是单松烯类和倍半萜烯。

Figure 1 GC-PTR-MS chromatograms of terpenes in the headspace of a beer sample. Data were acquired with a Fast GC coupled to a Vocus 2R PTR-TOF.  The overall analysis time was approximately 15 min. Beer headspace was sampled for 30 s before injection into the Fast GC column that was then ramped from room temperature to 225°C.
图1.啤酒顶空样品中萜烯的GC-PTR-MS色谱图。数据由耦合快速气相色谱(fast GC)的Vocus 2R PTR-TOF采集,总的分析时间约为15分钟。对啤酒样品进行30s的顶空采样,随后注射进气相色谱柱,升温程序将色谱柱从室温升温至225℃。
Figure 2. Mass spectral separation of terpenes from isobaric species.   In addition to the need for chromatographic separation of isomers, accurate characterization of terpenes (or other compound classes) by GC-PTR-MS requires that the mass analyzer can resolve any co-eluting compounds that have identical nominal mass and accurately identify species of interest based on exact mass.  For example, these data show that at retention time 640 seconds the Vocus 2R resolves multiple compounds at nominal mass 137 Th and treats only the peak at 137.1325 Th as monoterpene signal.
图2. 萜烯和同量异位化合物谱图鉴别。因采用的是快速色谱分离法,精确的定量萜烯(或其他化合物种)还需能分辨出同时洗脱出的同量异位化合物,并根据精确质量来准确的确定物种种类。如图中所示,在保留时间640s时Vocus 2R记录到名义质量137 Th的多个峰,其中只有137.1325的峰是来自于单萜的信号。

图2展示了TOF对于同洗脱出的同量异位VOCs的定性分析能力。图1中观测到的较多的色谱峰分别是单松烯类(红色)和倍半萜烯类(蓝色)。

同分异构体的基线分离让随后的定性定量分析变得更加容易。快速色谱分离和监测这些痕量待测物主要归功于Vocus PTR-TOF的快速响应(每秒10张谱图)和市场领先的高灵敏度(10000 cps/ppbv)。

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