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Published March 16, 2008 | metadata_only
Journal Article

Experimental and Theoretical Investigation into the Correlation between Mass and Ion Mobility for Choline and Other Ammonium Cations in N_2


A number of tertiary amine and quaternary ammonium cations spanning a mass range of 60−146 amu (trimethylamine, tetramethylammonium, trimethylethylammonium, N,N-dimethylaminoethanol, choline, N,N-dimethylglycine, betaine, acetylcholine, (3-carboxypropyl)trimethylammonium) were investigated using electrospray ionization ion mobility spectrometry. Measured ion mobilities demonstrate a high correlation between mass and mobility in N_2. In addition, identical mobilities within experimental uncertainties are observed for structurally dissimilar ions with similar ion masses. For example, dimethylethylammonium (88 amu) cations and protonated N,N-dimethylaminoethanol cations (90 amu) show identical mobilities (1.93 cm^2 V^(-1) s^(-1)) though N,N-dimethylaminoethanol contains a hydroxyl functional group while dimethylethylammonium only contains alkyl groups. Computational analysis was performed using the modified trajectory (TJ) method with nonspherical N_2 molecules as the drift gas. The sensitivity of the ammonium cation collision cross sections to the details of the ion−neutral interactions was investigated and compared to other classes of organic molecules (carboxylic acids and abiotic amino acids). The specific charge distribution of the molecular ions in the investigated mass range has an insignificant affect on the collision cross section.

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© 2008 American Chemical Society. Received 7 September 2007. Accepted January 9, 2008. Published online 16 February 2008. Published in print 15 March 2008. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA), the Noyes Laboratory of Chemical Physics, California Institute of Technology, and the Material and Process Simulation Center, Beckman Institute, California Institute of Technology. Financial support through NASA's Astrobiology Science and Technology Instrument Development, Planetary Instrument Definition and Development, and Mars Instrument Development programs is gratefully acknowledged. We appreciate the support provided by the Mass Spectrometry Resource Center in the Beckman Institute. The authors greatly appreciate Prof. Martin Jarrold at Indiana University Bloomington for generously allowing us to use and modify the Mobcal program. Hyungjun Kim and Hugh I. Kim contributed equally to this work.

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August 19, 2023
August 19, 2023