Enhancement of Characteristics of Field Asymmetric Ion Mobility Spectrometer with Laser Ionization for Detection of Explosives in Vapor Phase

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/cm(3) 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/cm(3). In this paper we compare a radioactive Ni-63 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 Ni-63 at optimal intensity of laser radiation for PETN and HMX of 3 x 10(7) W/cm(2) and 2.5 x 10(7) W/cm(2), respectively. Limits of detection were estimated: 3 x 10(-15) g/cm(3) for RDX, 8 x 10(-15) g/cm(3) for PETN and less than 3 x 10(-15) g/cm(3) 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.