Experimental study of the effect of temperature on ion cluster formation using ion mobility spectrometry
ABSTRACT Ion mobility spectrometry offers a robust and effective technique to study ion clusters in ambient conditions. Here, we have experimentally studied the influence of temperature on the positive ion cluster formation of 2-propanol vapor in air, along with parallel measurements for n-butyl acetate vapor in air. For both of these low proton affinity compounds in the ppm concentration range, temperatures below 0 °C tend to favor formation of dimers and trimers. The measurements indicate that approximate estimations for the fractions of these n-mers (n > 1) in the ion spectra, can be obtained by classical theory for ion induced nucleation. Presence of natural background vapors however slightly blurs the data, especially for the fraction of monomers, so that accurate prediction of the fractions of n-mers in the spectra would require more accurate information on the gas composition. The findings concerning thermal behavior of ions help to understand better ion phenomena also in field conditions.
SourceAvailable from: Devendraa Siingh
International Journal for Ion Mobility Spectrometry 12/2014; 17(3-4):117-124. DOI:10.1007/s12127-014-0157-5
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ABSTRACT: The aim of this work is to investigate the effects of various parameters on the mobility of NH4+ by use of an ion mobility spectrometer that is equipped with a corona discharge ionization source at atmospheric pressure. The reduced ion mobility values of NH4+ were measured in carbon dioxide, argon, nitrogen and helium as a function of temperature and E/N, the ratio of the electric field strength to the gas number density. The drift time of the ion in the different drift gases depends upon the ion-neutral interaction potentials that determine the collision cross-sections of the ion-drift gas systems, which includes a dependence upon the polarizabilities of the drift gases. The results of this research show that, under the same drift cell conditions, the reduced ion mobilities of NH4+ in the drift gases decrease in the order: He >> Ar >= N-2 > CO2. We also investigated temperatures between 25 and 225 C to study the effect on the reduced ion mobilities of NH4+ in the different drift gases. The reduced mobility was increased by increasing the temperature, which is attributed to break down of clusters at high temperature. We found the reduced ion mobility of NH4+ does not change with increasing E/N in Ar, N-2 and CO2, while it decreases in He.International Journal of Mass Spectrometry 09/2014; 370. DOI:10.1016/j.ijms.2014.06.014 · 2.23 Impact Factor