Development of a proton-transfer reaction ion trap mass spectrometer: Online detection and analysis of volatile organic compounds

The development of a new proton-transfer reaction ion trap mass spectrometer (PIT-MS) from a commercially available ion trap system is presented and the advantages of using an ion trap over a quadrupole mass filter are explored. For our PIT-MS we determine the optimal kinetic energy parameter E/N (95 Td) to be significantly lower than for the more conventional proton-transfer reaction mass spectrometer (PTR-MS) (120 Td) with a quadrupole mass filter. This gives a theoretical increase in sensitivity of ∼25% with respect to the generally used 120 Td. The limits of detection of the PIT-MS are still one order of magnitude higher than for the PTR-MS system, but better detection electronics are thought to improve this in the near future. The PIT-MS system is tested in a comparison with our PTR-MS on measurements of volatile compounds from an Elstar apple, where we show the time behavior and concentration determination of the PIT-MS to be reliable. In this comparison, we also show the applicability of and problems related to the use of collision induced dissociation (CID) analysis for the identification of compounds. The lower degree of fragmentation upon proton transfer is identified as an additional advantage of the use of low E/N-values.