Ion mobility spectrometry (IMS) was a technique originally applied for the detection of trace compounds. 1-3 IMS has been widely used to detect chemical warfare agents, 4-6 explosives, [7][8][9][10] and illegal drugs 10-13 since it combines both high sensitivity (detection limits down to the ng/L range to pg/L range, ppb range and ppt range) and relatively low technical expenditure with high-speed data acquisition. The time required to acquire a single spectrum is in the range of several tens ms. The working principle is based on the drift of ions at ambient pressure under the influence of an external electric field. 14-20 IMS works in a similar way to a time-of-flight mass spectrometer (TOFMS). The major difference is that TOFMS requires a vacuum but IMS does not. The mean free path of the ions in IMS is very smaller than in TOFMS. A typical IMS is comprised of an ionization source associated with an ion reaction chamber, an ion drift tube, an ion/molecule injection shutter placed between the ion reaction chamber and the ion drift tube, and an ion collector (detector, Faraday plate). An ion swarm drifting under the electric field experiences a separation process based on ions with different masses or structures having different drift velocities. Collecting these ions on a Faraday plate delivers a time-dependent signal corresponding to the mobility of the arriving ions. This ion mobility spectrum contains information on the nature of the different trace compounds present in the sample gas.Mass spectrometry is an important tool for the structural analysis of unknown chemicals. Soft ionization techniques such as matrix-assisted laser desorption and ionization (MALDI) and atmospheric pressure ionization (API) have been used for determination of molecular weight of an analyte. [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are the most currently used as API sources. In APCI, a corona discharge makes solvent reactant ions that are used to ionize the analyte by chemical ionization. [31][32][33][34] Solvent and analyte are vaporized by pneumatic nebulization. APCI relies upon gas-phase ion-molecule reactions to place a charge on neutral analytes, so it is especially important to understand these reactions. The solvent-derived ions serve as reagents for proton transfer ionization.Cocaine is a powerfully addictive drug because of its instantaneous and overwhelming effects on the central nervous system. It is generally analyzed by gas chromatography/mass spectrometry (GC/MS), liquid chromatography/mass spectrometry (LC/MS), GC, or LC. Recently, it has been analyzed using IMS. 11,[35][36][37] Lu and coworkers 35 analyzed cocaine and its metabolites, benzoylecgonine and cocaethylene in urine using solid phase extraction (SPE) coupled with IMS, and reported that the detection limits of benzoylecgonine and cocaethylene are 10 ng/mL (10 ppb) and 4 ng/mL (40 ppb), respectively. Dussy and coworkers 36 examined the validation of a qualita...

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Explosives containing nitro groups are nitroaromatic compounds, nitrate esters, and nitroamines.1 Dinitrotoluenes, 1,3,5-trinitrobenzene, and 2,4,6-trinitrotoluene (TNT) belong to the nitroaromatic compounds. Pentaerythritol tetranitrate (PETN) is a representative nitrate ester compound and the nitroamine explosives include 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine.Mass spectrometry is a good analytical technique for detection of explosives. Gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) are generally used for analysis of explosives.2-7 Atmospheric pressure chemical ionization (APCI) is a popular ionization source for analysis of explosives using LC/MS. In the previous work, 7 detection limit of PETN in APCI-MS was analyzed. Ion mobility spectrometry (IMS) has been widely used to detect explosives, [8][9][10][11][12] because it has high sensitivity and highspeed data acquisition. The time required to acquire a single IMS spectrum is several tens of milliseconds and the working principle of IMS is based on the drift of ions at ambient pressure under the influence of an external electric field. 13-19A typical IMS is comprised of a sampling region, an ionization source, an ion/molecule injection shutter, an ion drift tube, and an ion detector. An ion swarm drifting under the electric field experiences a separation process based on the different masses and structures. The ion mobility spectrum contains information on the nature of the different trace compounds present in the sample gas. Popular ionization sources used in IMS are 63 Ni ionization (β-ionization) and corona discharge ionization. The corona discharge ionization source is relatively new ionization method. 20 The 63 Ni ionization source has low electron energy and its applications are restricted to the determination of aromatic and unsaturated compounds. The corona discharge ionization can be used for ionization of a broad range of different classes of chemical compounds. 7,[21][22][23] In IMS, the ion mobility (K, cm 2 /V s) is defined by Eq. (1)where v d is the drift velocity of ion (cm/s), E is the electric field (V/cm), L is the drift distance of ion (cm), and t d is the drift time of ion in the drift region (s). The drift time of ion in IMS is influenced by the pressure and temperature of the drift region. The reduced ion mobility (K 0 ) is the pressure and temperature-corrected mobility. The reduced ion mobility is defined by Eq. (2)