| Over the past ten years, the world has been stunned and outraged by a series of attacks on civilian targets that used explosive devices. These attacks led to widespread demands for identification of the perpetrators, along with calls for improved security measures to prevent such incidents in the future. Detection techniques such as X-ray scanners, Raman spectroscopy, Terahertz spectroscopy and ion mobility spectrometry are currently in use or under development; however, none of these techniques are appropriate for all necessary applications. High-field asymmetric-waveform ion mobility spectrometry (FAIMS) coupled to a mass spectrometer is an alternative technique that provides improvements to mass spectral signal-to-noise, orthogonal/complementary ion separation to mass spectrometry, enhanced ion and complexation structural analysis, and potential for rapid analyte quantitation.;The primary goal of this research is to contribute to the understanding of ionization by an atmospheric pressure ionization (API) source and ion behavior in a FAIMS cell to assist the future development of a portable explosive detector to investigate explosives in the field. In this work, the ionization mechanism of two API sources, atmospheric pressure chemical ionization (APCI) and distributed plasma ionization source (DPIS), are discussed. The spectra of eleven explosives ionized by both sources were collected and characterized. The results show that APCI provides a consistent and simple ionization, while DPIS presents more discrimination by various ion fragments and is more amenable for monitoring a certain classes of explosives in the field. Variation in FAIMS parameters, such as dispersion voltages (DV), compensation voltage (CV) scan rate, curtain gas flow rate, carrier gas composition, and electrode temperature, was explored for their effect on explosive ions. A systematic evaluation of the performance of API-FAIMS-MS demonstrates sensitivity at the picogram level, short detection time (30 seconds), and excellent resolution such that isomers of the same explosive can be successfully resolved. The results from these studies with the laboratory procedure show promise for FAIMS to be used as an explosive detector that presents a sensitive, selective, specific and rapid technique. |
