Behavior and evaluation of tetraalkylammonium bromides as instrument test materials in thermal desorption ion mobility spectrometers

Ion mobility spectrometers have found widespread use for the screening of explosives, chemical warfare agents, and illicit drugs. These instruments often rely on drift-time calibrants to perform qualitative identification. Such calibrants are suitable to determine the reduced mobility of compounds, but may not necessarily provide information on instrument performance. These calibrants are often internal and behave in a fashion similar to that of analytes in terms of sensitivity to a variety of instrumental and environmental variations. Ideally, test materials used to evaluate instrument performance would be insensitive to these changes. Current calibrants are sometimes not designed to satisfy these requirements, and although several instrument test materials are also in use, a consensus has not been reached on best practices. A homologous series of tetraalkylammonium salts has been proposed as one alternative instrumental test material set and has been successfully used for electrospray ion mobility spectrometry (IMS)-MS experiments. This study extends these analyses to thermal desorption IMS instruments. The reduced mobility (K ) values for these compounds, measured on a thermal desorption IMS instrument, are reported and are similar to those reported for electrospray IMS. The variability of daily instrument response to these compounds is small, further supporting their use as test materials. The ionization behavior and thermal profile of the compounds in the thermal desorption process are discussed.