Explosive detection has turned to a worldwide concern in recent years due to the increasingly serious international armed conflicts and terrorism. For homeland security and residents' personal safety, people paid more attention to detection and identification of explosives with physical and chemical technologies, among which ambient MS technology is of clear advantage in trace explosive determination.
As to plasma-based ambient MS methods, this capability has been shown in DART, DAPCI, FAPA, DBDI, and LTP. For example with DART (Rowell et al., 2012), seven common explosives, including TATP, Tetryl, TNT, TNG, PETN, RDX, and HMX, presented in spiked latent marks have been tested in pg range. In the study, the explosives were successfully detected on several surfaces such as finger, paper, plastic bag, metal drink can, wood laminate, adhesive tape, and white ceramic tile to demonstrate DART-MS an effective explosive detector. The capability of DAPCI in explosive detection was first confirmed by Cooks and coworkers (Takats et al., 2005; Song & Cooks, 2006). In a latter application (Song & Cooks, 2006), DAPCI and APCI were used to detect nitro-aromatic explosives by monitoring their ion/molecule reaction products ([M+CN]−, [M+CH2CN]−, [M+OH]−, [M+OOH]−) with reagent ions produced from acetonitrile and air. DAPCI has also been used for peroxide-based explosives that involve HMTD and TATP (Cotte-Rodriguez et al., 2008), where 15 ng of each explosive deposited on paper in a total area of 1 cm2 was detected with or without ammonium acetate added as dopant to the carrier gas (N2). Zhang and coworkers have reported the application of DBDI to detect trace amounts of explosives on solid surfaces (Na et al., 2007a) with limit of detection in the 1 ng to pg range. The experiment setup includes a pin-to-plate configuration DBD source and He used as the plasma gas at the flow rate of 150 mL min−1, although Ar, N2, and air also worked. The matrices have little influence on the detective performance because the RSD to detect TNT on five different matrices is 5.57%. The use of LTP to analyze RDX, TNT, and PTEE with a limit of detection at 5 pg has been described (Harper et al., 2008). Zhang et al. (2009) soon improved the LOD of the same explosives to the low fg range on conductive and non-conductive substrates. Further illustrations of ultra-trace amount analyses of more than 13 common explosives and explosives-related compounds have established a place for LTP-MS in this field (Garcia-Reyes et al., 2010). An initial result on the combination of a portable mass spectrometer to LTP for in situ trace explosive analysis has been presented recently (Dalgleish et al., 2012). This trial permitted the detection of 100 ng of PETN, RDX, and Tetryl only in 1 min with air supplied by a small diaphragm pump that served as the working gas. As mentioned earlier (Shelley, Wiley, & Hieftje, 2011), the pin-to-capillary configuration FAPA has also been used to identify PETN and latent fingerprint of RDX, the low amol to fmol detection limits, easily identified mass spectra make this novel method attractive for homeland security applications. However, applications of those ambient MS methods in the field of explosive detection are still under development, because few reports have dealt with the linear issue of quantification.