External second gate Fourier transform ion mobility spectrometry: parametric optimization for detection of weapons of mass destruction

Ion mobility spectrometry (IMS) is recognized as one of the most sensitive and robust techniques for the detection of narcotics, explosives and chemical warfare agents. Increasing threat of terrorist attacks, the proliferation of narcotics, Chemical Weapons Convention treaty verification as well as humanitarian de-mining efforts have mandated that equal importance be placed on the analysis time as well as the quality of the analytical data. IMS unrivaled when both speed of response and sensitivity have to be considered. The problem with conventional (signal averaging) IMS systems is the fixed duty cycle of the entrance gate that restricts to less than 1%, the number of available ions contributing to the measured signal. Furthermore, the signal averaging process incorporates scan-to-scan variations that degrade the spectral resolution. With external second gate Fourier transform ion mobility spectrometry (FT-IMS), the entrance gate frequency is variable and can be altered in conjunction with other data acquisition parameters to increase the spectral resolution. In addition, with FT-IMS the entrance gate operates with a 50% duty cycle and so affords a 7-10 fold increase in sensitivity. Recent data on high explosives are presented to demonstrate the parametric optimization in sensitivity and resolution of our system.