Abstract
Ion mobility spectrometry instrumentation today is widespread in the area of transport security and counterterrorism. This method of detection of explosive substances is highly appreciated for the existence of portable detectors capable of detecting concentrations of 10−13–10−14 g/cm3 at atmospheric pressure using traditional ionization methods including corona discharge and beta radiation. However, low vapor pressure of some explosives imposes requirements on limit of detection (LOD) down to 10–15‒10−16 g/cm3. In this paper we compare a radioactive 63Ni ionization source with a laser ionization source and reveal the parameters of laser ionization of a group of explosives, namely trinitrotoluene (TNT), cyclotrimethylene-trinitramine (RDX), cyclotetramethylene-tetranitramine (HMX) and pentaerythritol tetranitrate (PETN), which can reduce the limit of detection of portable devices. A laser ionization source can provide a higher signal to noise ratio than radioactive 63Ni at optimal intensity of laser radiation for PETN and HMX of 3 × 107 W/cm2 and 2.5 × 107 W/cm2, respectively. Limits of detection were estimated: 3 × 10−15 g/cm3 for RDX, 8 × 10−15 g/cm3 for PETN and less than 3 × 10−15 g/cm3 for HMX. These results are promising to further improve the capabilities of detectors of low volatility explosives without sacrificing portability, light weight and reasonable cost of the laser source.
Highlights
State-of-the-art detectors of explosives are developed nowadays involving a wide range of physical and chemical methods including gas-analytical, nuclear–physical, electromagnetic and biological.Оne of the most challenging problems is detection of explosives in the vapor phase
Ionization mechanisms of nitro-compounds depend on ionization conditions
The best solution will be a balance of laser intensity of about 4 × 107 W/cm2, with a beam size covering enough space inside the balance of laser intensity of about 4 × 107 W/cm2, with a beam size covering enough space inside the ion source and a maximum repetition rate at a reasonable price, size and weight of the laser source
Summary
Оne of the most challenging problems is detection of explosives in the vapor phase. The limit of detection (LOD) of 10−14 g/cm for trinitrotoluene vapors (TNT) was obtained by registering the luminescence of NO-fragments of fragmented TNT molecules during the detection time of 10 s from a distance of several meters. The developed system is bulky, and laser remote irradiation is not safe, so the method is not convenient for practical usage. Another approach to detecting vapors of explosives involved their concentration on meshes with subsequent thermal desorption and analysis in a portable chromatograph with polycapillary columns and air as carrier gas; an LOD of 10−14 g/cm was obtained in this case [2]. The authors estimated the LOD of the system as 250 ppm with an integration time of 100 s
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