Dependence of polyatomic ion mobilities on ionic size

Abstract

Hydrogen bond and residence dynamics of ion-water and water-water pairs in supercritical aqueous ionic solutions: Dependence on ion size and density An improved method to estimate ionic size for calculating polyatomic ion mobilityThe ion mobilities of 11 negative ions in nitrogen have been measured using a plasma chromatograph. The ions range from small negative ions such as NO z to large organic ions such as the parent negative ion of I-naphthaldehyde, (CjjHgO)-. The reduced ion mobilities for these negative ions, in addition to previously published ion mobilities of protonated hydrocarbons, were compared with the Langevin theory of ion mobility. The hard sphere average collision cross section between the ion and the neutral carrier gas N, was estimated using two models: (I) static model where the ion is nonrotafing and (2) 'rotational model where the ion is assumed to be rotating rapidly. Comparison of the calculated reduced ion mobilities with the experimental values reveals that the experimental collision cross sections are intermediate between those calculated using these two models. The experimental and calculated ion mobilities gave the best agreement using the mean collision cross section for the static and rotational models. The average deviation between the experimental and calculated ion mobilities was 4% for a total of 21 positive ions and 14 negative ions. These results suggest (1) the ion size is the dominant parameter affecting the ion mobility of large molecular ions and (2) the rotation of nonspherical molecular ions must be considered.4994

Scaling of the resolving power and sensitivity for planar FAIMS and mobility-based discrimination in flow- and field-driven analyzers

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