International Symposium on Hyphenated Techniques in Chromatography and Separation Technology (HTC-13) edition:13 location:Brugge, Belgium date:28-31 January 2014
The monoterpene alcohol linalool has been considered as a key character impact compound and analytical marker for measuring and predicting hoppy aroma of beer. Accurate quantitative determination of linalool in the complex flavour profile of finished beer is however not evident and requires high sensitivity and selectivity of the analytical method.
For analytical profiling of esters and fusel alcohols in finished beers, a methodology based on HS-SPME and GC-ion trap MS is applied routinely in our laboratory. However, co-elution of linalool and 2-phenylethanol hampers precise determination of the linalool level. The challenge of this study is to adequately quantify linalool in the complex beer aroma profile without changing extraction conditions or stationary phase of the capillary column.
Selected ion monitoring (SIM) or tandem mass spectrometry (MS/MS) are straightforward possibilities to achieve high selectivity on the detector level and therefore their appropriateness for precise quantification of linalool in beer was evaluated. To discriminate linalool and 2-phenylethanol, the fragment ions at m/z=93 and m/z=136 were selected for SIM, while for MS/MS, the mass fragment ion at m/z=121 was selected for further fragmentation via collision-induced dissociation (CID). The fragmentation of this precursor ion into daughter ions was investigated by gradually increasing the collision energy in the ion trap. A different fragmentation pattern of the precursor ion at m/z=121 originating from linalool or 2-phenylethanol was observed and the characteristic daughter ion at m/z=105 in the MS/MS spectrum of linalool was selected for quantitative determinations. The accuracy of the SIM and MS/MS method was substantiated by analyzing beer samples spiked with linalool. The results show accurate quantification of linalool in beer via MS/MS although linalool co-elutes with 2-phenylethanol. SIM did not overcome the problem of co-elution. Good linearity (r=0.9996) is observed for the MS/MS method (concentration range: 0 to 500 µg/L). The coefficient of variation is less than 1.3% while the LOD is determined at 0.17 µg/L. The presented methodology was applied to fresh and aged beers. Clear differences were observed for the linalool levels in fresh beers and, remarkably, the levels remained practically constant upon beer ageing.
The poster presents a new and specific analytical method for highly selective, accurate quantification of linalool, a recognised key character impact compound and analytical marker for the intensity and quality of hoppy aroma of beer. Evidently, the presented method can be implemented to determine the linalool level in other matrices (e.g. essential oils, cosmetics, perfumes, soaps, ...).