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15 August 2003 Enhanced sensitivity and selectivity in a dual cell ion mobility spectrometer
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While ion mobility spectrometry (IMS) has been used as a portable trace vapor detector, these handheld systems suffer from poor selectivity. Their low resolution makes confident identification of chemical species difficult. One major application for these IMS systems is in Homeland Defense. IMS systems are fielded for the detection of chemical warfare agents, explosives, narcotics, and other hazardous chemicals. Recently, a novel signal processing methodology using wavelet filtering, statistical evaluators, and genetic algorithms was demonstrated to improve sensitivity and specificity of an ion mobility spectrometer. Previous work involved a single (single polarity) IMS cell. Since both positive and negative ions are created in the same environment and a common sample interface is used for the dual IMS system, there is cross talk between the positive and negative cell. Typically, this cross talk provides little information on the identity of the chemical species present. However, using this new methodology, valuable sample information is obtained. Moreover, ion beam modulation has been incorporated to allow for the ion beam to be broken up into discrete packets. The modulation allows the rejection of common background interferents. This paper will present the process of using cell cross talk, ion beam modulation, and application and extension of the signal processing methodology. The application to field instrumentation will also be discussed.
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Matthew Todd Griffin, Jack E. Fulton Jr., Robert F. McAtee, Rong Gao, and Lefteri H. Tsoukalas "Enhanced sensitivity and selectivity in a dual cell ion mobility spectrometer", Proc. SPIE 5085, Chemical and Biological Sensing IV, (15 August 2003);

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