Temperature dependence of ion mobility signals of halogenated compounds

Ion mobility spectrometry (IMS) as handheld and transportable sensor technique permits the sensitive detection of halogenated compounds with importance in environmental monitoring and process control. The negative ion mobility spectra mostly show one product ion peak which can be attributed to (H2O)nX− ions due to dissociative electron attachments. For minimizing memory effects and contaminations, modern ion mobility spectrometers work at elevated temperatures. In this paper, we investigated the influence of temperature on peak position, resolution and relative abundance of ions formed from halogenated substances. Elevated temperatures affect the peak position in different way. For fluorine- and chlorine-containing product ions, changes in hydration and clustering have a considerable influence on peak position, while these processes are of minor importance for bromine- and iodine-containing product ions. In these cases, the drift time differences mainly result from differences in drift behavior due to differences in gas density, the mean free path of ions and different collision rates. The drift time shift with elevated temperatures provides an enhanced peak-to-peak resolution. Improved separation efficiency can therefore be established with increased temperatures for negative product ions of halogenated compounds. Furthermore, an enhanced sensitivity was found for all compounds with increasing temperatures. However, independent on the temperature, the order of sensitivity is mainly determined by the bonding state of halogen atoms within the molecules.