Thermal Ionization Ion Mobility Spectrometry of Alkali Salts

Abstract

Positive and negative thermal ionization ion mobility spectra (TI-IMS) of some sodium and potassium halides are reported here. The data provide the first measurement of the thermal ionization ion mobility spectrometry of inorganic compounds. A thin Nichrome filament was used as a thermionic ionization source. Sample was directly deposited on the filament, where it was heated and ionized. Each salt produced a different ion mobility pattern, but all sodium salts spectra were common in their first peak. This peak differs from the common peak observed in the spectra of potassium salts. The drift time of the second peak in all spectra was found to be linearly dependent on the size of the counteranion of the salt. Negative thermal ionization ion mobility spectra of alkali halides were also observed. An alkali halide salt (MX), in general, produced its own anion as well as some heavier ions that are thought to be hydrated X^-(MX)_n species. The capability of the method in quantitative analysis was demonstrated by measuring potassium impurity in sodium bromide. A detection limit of 0.01% K⁺ in NaBr and a linear rage of 3 orders of magnitude were obtained. The results from this study suggest that TI-IMS has potential as a field technique for the detection of some elements in samples.