Investigation of temperature, electric field and drift-gas composition effects on the mobility of NH4+ ions in He, Ar, N2, and CO2

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≥N2>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, N2 and CO2, while it decreases in He.