Combining miniaturized ion mobility spectrometer and metal oxide gas sensor for the fast detection of toxic chemical vapors

Combined use of miniaturized non-conventional aspiration-type ion mobility spectrometer (IMS; referred as ion mobility cell, IMCell) and metal oxide semiconductor (MOS) gas sensor for detecting toxic chemical vapors in a continuous 1-2 l/min flow-through system is demonstrated. The data for 38 chemical vapors show that the detection limits of IMCell sensor follow extraordinary well over several orders of magnitude the given threshold limit values (TLVs) of vapor concentrations in the working environments providing thus good specificity to toxic chemicals. The IMS patterns for eight chemicals are presented and the shape of patterns are discussed through theories related to ionization and ion mobility in ambient air. As demonstrated with exposures to 30-300 ppm methyl tert-butyl ether (MTBE) one of the main roles of the MOS sensor is to compensate the strong decreasing influence of humidity to the IMCell sensor signal by providing sensitive output regardless of humidity to some toxic organic compounds. Furthermore, it is also demonstrated that the chemical recognition of toxic substances by IMCell sensor is improved when the signal from the MOS sensor is available for the pattern recognition. The long-term stability studies were carried out, too, and the results indicate that minimum 3000 h operational lifetime can be obtained for the whole detector system. (C) 2003 Elsevier Science B.V. All rights reserved.