Assessment of the feasibility of the use of conductive polymers in the fabrication of ion mobility spectrometers

The development of an ion mobility spectrometer with an injection molded plastic drift tube made from carbon-loaded nylon and the cyclo-olefinpolymer Zeonex is described. Thermogravimetric assessment combined with headspace analysis by ion mobility spectrometry and gas chromatography−mass spectrometry indicated that Zeonex encapsulated carbon-loaded nylon could be used to fabricate a snap-together injection molded stacked ring drift tube, 4.25 cm long that could be substituted for a conventional wire-wound heated ceramic drift tube of the same length into a high temperature ion mobility spectrometer. Temperature stability experiments indicated that such a combination of polymers produced stable water-based reactant ion peaks [(H2O)nH]+ up to a temperature of approximately 50 °C. Above this temperature, ammonia appeared to outgas, resulting in the production of [(H2O)n(NH4)mH]+ type species before, at higher temperatures, the release of oligomeric entities suppressed resolved ion responses. Surface charging effects were also observed, and over a period of continuous operation of 4 h, these caused suppression of the signal intensity (1.11−0.954 V) and an apparent mobility shift in the observed responses (K0 = 1.86−1.90 cm2 V−1 s−1). Substituting nylon, a polymer with a significantly lower surface resistivity, for the Zeonex demonstrated how surface charging phenomena could be managed though control of surface resistivity in future polymer formulations. The device was challenged successfully with test atmospheres of hexan-1-ol (K0 = 1.66 cm2 V−1 s−1 (monomer) and 1.32 cm2 V−1 s−1(dimer)) and dimethylmethyl phosphonate (K0 = 1.70 cm2 V−1 s−1 (monomer) and 1.44 cm2 V−1 s−1 (dimer)). The potential advantages of developing polymeric systems using more advanced polymer formulations are discussed.