Influence of Smear Matrix Type on Detection Efficiencies of Explosives in Corona Discharge‐Ion Mobility Spectrometer

Abstract

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)

The influence of different types of reactant ions on the ionization behavior of polycyclic aromatic hydrocarbons in corona discharge ion mobility spectrometry

“…The use of a smear matrix for IMS analysis is a simple and useful sampling method for on‐site detection 30,31,53–55 . The solid‐state analyte molecules are simply introduced into the ionization region from the sample inlet where they can react with RIs.…”

“…The same group has also described the use of a miniature handheld rectilinear ion trap mass spectrometer that would be suitable for on‐site detection of PAHs, but this instrument also needs a large battery to operate the vacuum system 28,29 . An ion mobility spectrometer is light enough to carry by hand, and these instruments have been used for the on‐site detection of hazardous chemicals such as explosives, drugs, and chemical warfare agents 30–34 . In a previous study, we examined the influence of different smear matrices on the ionization efficiencies of some PAHs in ion mobility spectrometry (IMS) 35 …”

Test method for vapor collection and ion mobility detection of explosives with low vapor pressure

“…Therefore, a simple and low‐cost method for explosive vapor collection is required. Swab and smear matrices are typically used for collecting solid‐state explosives for IMS detection 34–37 . Furthermore, they are simple and affordable.…”

“…Swab and smear matrices are typically used for collecting solid-state explosives for IMS detection. [34][35][36][37] Furthermore, they are simple and affordable.…”