Rapid analysis of selected beer volatiles by atmospheric pressure chemical ionisation-mass spectrometry

For rapid determination of some key aroma compounds in fermented beer, headspace was analysed by atmospheric pressure chemical ionisation-mass spectrometry (APCI-MS) and the ion intensities used to predict beer aroma content. To achieve this aim, potential interference from ethanol during ionisation was overcome by using ethanol as the charge transfer reagent ion and the cone voltage was varied to induce fragmentation of the compounds and provide more information to build a robust correlation between headspace analysis and concentration in the beer itself. Ten solutions containing different ethanol concentrations (0.5-5 mL/100 mL), and different concentrations of the key aroma compounds, were analysed by APCI-MS at cone voltages between 12 and 21 V. Linear regression models were created for each compound to correlate the ion intensities measured by APCI-MS at the different cone voltages with the in-solution concentration of the compounds (average R-2=0.95). Of the 14 compounds studied, six could be quantified unequivocally, six compounds were quantified as pairs of isobaric compounds and two could not be reliably analysed. To test the linear regression model equations, the headspace above samples of fermenting wort or commercial beer and cider products were analysed by APCI-MS and the predicted concentrations of twelve aroma compounds in the samples were compared with the actual values measured by extraction and GC-MS analysis: correlation coefficients ranged between 0.753 and 0.979. (C) 2010 Elsevier B.V. All rights reserved.