The full references are:
A. Hansel, A. Jordan, R. Holzinger, P. Prazeller W. Vogel, W. Lindinger, Proton transfer reaction mass spectrometry: on-line trace gas analysis at ppb level, Int. J. of Mass Spectrom. and Ion Processes, 149/150, 609-619 (1995).
W. Lindinger, A. Hansel and A. Jordan, On-line monitoring of volatile organic compounds at pptv levels by means of Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS): Medical applications, food control and environmental research, Review paper, Int. J. Mass Spectrom. Ion Proc., 173, 191-241 (1998).
A. Jordan, S. Haidacher, G. Hanel, E. Hartungen, J. Herbig, L. Märk, R. Schottkowsky, H. Seehauser, P. Sulzer, T.D. Märk: An online ultra-high sensitivity proton-transfer-reaction mass-spectrometer combined with switchable reagent ion capability (PTR+SRI-MS), International Journal of Mass Spectrometry 286 (2009), 32-38.