Direct mass spectrometry of complex volatile and non-volatile flavour mixtures

There are several flavour analyses that require very rapid analysis of a complex mixture. Monitoring flavour release from foods during eating is one example, requiring a sensitive (mug/kg), rapid (millisecond) response to a wide range of compounds (alcohols, esters, heterocycles, etc.). Another example is in plant breeding to improve plant flavour where large numbers of plant products (fruits, leaves, etc.) need rapid analysis (typically within 2-4 h) to prevent significant variation due to postharvest metabolic changes. Conventional chromatography-MS of such complex mixtures to resolve all components is slow (30-60 min per sample) making analysis of large numbers of samples an unrealistic task. Direct MS techniques use no chromatography but sample the mixture of compounds directly into the source and resolve the ions by mass alone. The key problems are potential suppression of ionisation in the source, leading to non-quantitative results and difficulties in unequivocal identification of compounds solely on the basis of their m/z values. It is possible to overcome these problems in some cases and obtain quantitative analyses under carefully controlled conditions. Examples of some successful direct MS techniques in the gas and liquid phase are presented with a discussion of their benefits and limitations. (C) 2002 Published by Elsevier Science B.V.