Real-time detection of IED explosives with laser ionization mass spectrometry

The ESSEX system (Extremely Sensitive and Selective Explosives detector) is a system that can be used for standoff or remote detection of suicide bombers at a distance of up to a few meters via the trace amounts of explosives present in vapor phase around explosives with a high vapor pressure. The ESSEX detection method is based on laser ionization mass spectrometry (LI-MS). Direct sampling of air with explosives in vapor phase will allow detection of explosives with relatively high vapor pressure, such as TATP (suspected to have been used in the recent suicide bombings in London as well as numerous suicide bombings in Israel) and EGDN (normally found in dynamite explosives such as the ones used in the Madrid bombings). The LI-MS method has a potential to detect all or nearly all explosives. For explosives with low vapor pressure (e.g. RDX, HMX, PETN, AN) it is probably necessary to sample particles as well. Other aspects of the future potential for this method are that the number of explosives that the method targets can be increased as needed. The method is very suited for data fusion and processing, making it possible to incorporate artificial intelligence (AI) into the system. The uniqueness of LI-MS methods lies in its low detection limit, possibility of real-time detection, its versatility regarding the number of possible substances to detect and its unique selectivity, leading to very few false alarms. The ESSEX concept is appropriate for indoor and outdoor applications, it is benign to humans and property and can be applied in an unnoticeable way. Laser ionization mass spectrometry and specifically resonance enhanced multi photon ionization (REMPI) is an ultra-sensitive, highly selective analytical technique that can identify and quantify vapor-phase constituents at parts-per-trillion (ppt) levels. The REMPI technique combines the principles of optical spectroscopy and mass spectrometry to provide a two-dimensional detection scheme that yields a high degree of chemical sensitivity and selectivity. This method has proven effective for the detection of one trace compound at ppt levels in the midst of others. The sensitivity and specificity for REMPI can be dramatically improved by using cooling with a supersonic jet based inlet. This cooling greatly simplifies the spectra, producing narrower and stronger electronic transitions and allows sampling directly from air. This paper describes the principles of LI-MS for standoff detection the trace amounts of explosives present in vapor phase around explosives with a high vapor pressure as well as the future potential of the method.