Low-Temperature Plasma Ionization Differential Ion Mobility Spectrometry

A low-temperature plasma (LTP) was used as an ionization source for differential ion mobility spectrometry (DMS) for the first time. This ionization source enhances the potential of DMS as a miniaturized System for on-site rapid monitoring. The effects of experimental parameters (e.g., discharge/carrier gas composition and flow rate, applied voltage) on the analysis of model aromatic compounds were investigated and discussed. It was found that the nature of reactant ion positive (RIP) is dependent on the discharge/carrier gas composition. The best response to the analyte was achieved when pure nitrogen was used as the discharge/carrier gas. The ability to perform analysis with zero helium consumption is especially attractive in view of the potential application of LTP-DMS for online (and on-site) monitoring. Analytical performance was determined with six environmentally relevant model compounds (benzene, toluene, ethylbenzene, p-xylene, 1,2,4-trimethylbenzene, and naphthalene) using LTP and directly compared to APPI and APCI (Ni-63) ionization sources. When LTP was coupled to DMS, calculated LOD values were found to be in the range of 35-257 ng L-1 (concentration in the carrier gas). These values are competitive with those calculated for two DMS equipped with traditional ionization sources (APPI, Ni-63). The obtained results are promising enough to ensure the potential of LTP as ionization source for DMS.