Abstract
We present studies of the ionization mechanism operative in the ambient pressure pyroelectric ionization source (APPIS), along with applications that include detection of simulants for chemical nerve agents. It is found that ionization by APPIS occurs in the gas-phase. As the crystal is thermally cycled over a narrow temperature range, electrical discharges near the surface of the crystal produce energetic species which, through reactions with atmospheric molecules, result in reactant ions such as protonated water clusters or clusters of hydroxide and water. Reactant ions can be observed directly in the mass spectrometer. These go on to react with trace neutrals via proton transfer reactions to produce the ions observed in mass spectra, which are usually singly protonated or deprotonated species. Further implicating gas-phase ionization, observed product distributions are highly dependent on the composition of ambient gases, especially the concentration of water vapor and oxygen surrounding the source. For example, basic species such as triethylamine are observed as singly protonated cations at a water partial pressure of 10 torr. At a water pressure of 4 torr, reactive oxygen species are formed and lead to observation of protonated amine oxides. The ability of the APPIS source to detect basic molecules with high proton affinities makes it highly suited for the detection of chemical nerve agents. We demonstrate this application using simulants corresponding to VX and GA (Tabun). With the present source configuration pyridine is detected readily at a concentration of 4 ppm, indicating ultimate sensitivity in the high ppb range.
Article PDF
Similar content being viewed by others
References
Neidholdt, E. L.; Beauchamp, J. L. Ambient pressure pyroelectric ion source for mass spectrometry. Anal. Chem. 2007, 79, 3945–3948.
McLuckey, S. A.; Glish, G. L.; Asano, K. G.; Grant, B. C. Atmospheric sampling glow discharge ionization source for the determination of trace organic compounds in ambient air. Anal. Chem. 1988, 60, 2220–2227.
Harrison, W. W.; Hess, K. R.; Marcus, R. K.; King, F. L. Glow discharge mass spectrometry. Anal. Chem. 1986, 58, 341A-356A.
Mason, R.; Milton, D. Glow discharge mass spectrometry of some organic compounds. Int. J. Mass Spectrom. Ion Processes 1989, 91, 209–225.
Carroll, D. I.; Dzidic, I.; Stillwell, R. N.; Haegele, K. D.; Horning, E. C. Atmospheric pressure ionization mass spectrometry: Corona discharge ion source for use in liquid chromatograph-mass spectrometer-computer analytical system. Anal. Chem. 1975, 47, 2369–2373.
Na, N.; Zhao, M.; Zhang, S.; Yang, C.; Zhang, X. Development of a dielectric barrier discharge ion source for ambient mass spectrometry. J. Am. Soc. Mass Spectrom. 2007, 18, 1859–1862.
Bayssie, M.; Brownridge, J. D.; Kukhtarev, N.; Wang, J. C. Generation of focused electron beam and X-rays by the doped LiNbO3 crystals. Nucl. Instrum. Methods Phys. Res. B 2005, 241, 913–916.
Geuther, J. A.; Danon, Y. Electron and positive ion acceleration with pyroelectric crystals. J. Appl. Phys. 2005, 97, 074109.
Brownridge, J. D.; Shafroth, S. M. Using static charge on pyroelectric crystals to produce self-focusing electron and ion beams and transport through tubes. J. Electrostat. 2005, 63, 249–259.
Kukhtarev, N.; Kukhtareva, J. D. T.; Bayssie, M.; Wang, J.; Brownridge, J. D. Generation of focused electron beam by pyroelectric and photogalvanic crystals. J. Appl. Phys. 2004, 96, 6794–6798.
Brownridge, J. D.; Shafroth, S. M. Pressure dependence of energetic (≤160 keV) focused electron beams arising from heated or cooled (LiNbO3) pyroelectric crystals. Appl. Phys. Lett. 2003, 83, 1477–1479.
Brownridge, J. D.; Shafroth, S. M. Self-focused electron beams produced by pyroelectric crystals on heating or cooling in dilute gases. Appl. Phys. Lett. 2001, 79, 3364–3366.
Brownridge, J. D.; Shafroth, S. M.; Trott, D. W.; Stoner, B. R.; Hooke, W. M. Observation of multiple nearly monoenergetic electron production by heated pyroelectric crystals in ambient gas. Appl. Phys. Lett. 2001, 78, 1158–1159.
Rosenblum, B.; Braulich, P.; Carrico, J. P. Thermally stimulated field emission from pyroelectric lithium niobate. Appl. Phys. Lett. 1974, 25, 17–19.
Geuther, J.; Danon, Y. High-energy X-ray production with pyroelectric crystals. J. Appl. Phys. 2005, 97, 104916.
Naranjo, B.; Gimzewski, J. K.; Putterman, S. Observation of nuclear fusion driven by a pyroelectric crystal. Nature 2005, 434, 1115–1117.
Geuther, J.; Danon, Y.; Saglime, F. Nuclear reactions induced by a pyroelectric accelerator. Phys. Rev. Lett. 2006, 96, 054803.
Steiner, W. E.; Clowers, B. H.; Haigh, P. E.; Hill, H. H. Secondary ionization of chemical warfare agent simulants: Atmospheric pressure ion mobility time-of-flight mass spectrometry. Anal. Chem. 2003, 75, 6068–6076.
Steiner, W. E.; English, W. A.; Hill, H. H. Separation efficiency of a chemical warfare agent simulant in an atmospheric pressure ion mobility time-of-flight mass spectrometer (IM(TOF)MS). Anal. Chim. Acta 2005, 532, 37–45.
Steiner, W. E.; Klopsch, S. J.; English, W. A.; Clowers, B. H.; Hill, H. H. Detection of a chemical warfare agent simulant in various aerosol matrixes by ion mobility time-of-flight mass spectrometry. Anal. Chem. 2005, 77, 4792–4799.
Riley, D. P. Ruthenium chloride catalyzed oxidation of tertiary amines to amine oxides with molecular oxygen. J. Chem. Soc., Chem. Commun. 1983, 24, 1530–1532.
Riley, D. P.; Correa, P. E. An unprecedented selective autoxidation of tertiary amines to amine oxides. J. Org. Chem. 1985, 50, 1564–1566.
Ma, S.; Chowdhury, S. K.; Alton, K. B. Thermally induced n-to-o rearrangement of tert-N-oxides in atmospheric pressure chemical ionization and atmospheric pressure photoionization mass spectrometry: Differentiation of N-oxidation from hydroxylation and potential determination of N-oxidation site. Anal. Chem. 2005, 77, 3676–3682.
Atkinson, R. Kinetics and mechanisms of the gas-phase reactions of the hydroxyl radical with organic compounds under atmospheric conditions. Chem. Rev. 1985, 85, 69–201.
Author information
Authors and Affiliations
Corresponding author
Additional information
Published online July 18, 2009
Rights and permissions
About this article
Cite this article
Neidholdt, E.L., Beauchamp, J.L. Ionization mechanism of the ambient pressure pyroelectric ion source (APPIS) and its applications to chemical nerve agent detection. J Am Soc Mass Spectrom 20, 2093–2099 (2009). https://doi.org/10.1016/j.jasms.2009.07.009
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1016/j.jasms.2009.07.009