ABSTRACT
Several methods for the real-time analysis of volatile compounds by mass spectrometry have been developed. Some of the earliest used atmospheric pressure chemical ionization (APcI) to measure volatiles in the breath during exhalation [1]. Others used electron impact mass spectrometers, interfaced to the gas phase via membranes [2]. More recently, further developments in APcI [3] and the emergence of proton-transfer-reaction mass spectrometry (PTRMS) [4] have further advanced our ability to monitor volatile compounds in real time. The unifying feature of all of these methods is the characteristic that all analytes enter the ionization region simultaneously: there is no chromatographic separation before detection. They all rely on the potential of the mass spectrometer to separate the analytes on the basis of mass to give them selectivity. Consequently, if two or more compounds occur at the same mass, then it may not be possible to distinguish between them by using these techniques. This situation becomes more difficult as the complexity of the system under analysis increases, as in the case of real foods. This can be highlighted by the fact that the majority of the 2500 or more aroma compounds that have been identified have even mass molecular weights between 70 and 190 da.
