Use of dopants for detection of vapors of explosives by laser field asymmetric ion mobility spectrometer

Abstract

Ion mobility spectrometry (IMS) today figures prominently among analytical methods for detection of explosives and is widely used for transport security. This method is highly appreciated for capability to distinguish low quantity of different types of explosives at atmospheric pressure. The main obstacle for sensing some kinds of explosives is their very low vapor pressure so that the limit of detection of state-of-the-art IMS instrumentation 10^-13 –10^-14 g/cm³ lacks at least an order of magnitude. In this paper we combine promising UV laser radiation along with application of organic compounds (dopants) to improve ionization efficiency and vapor detection capabilities of IMS. Dopants with low ionization energy (toluene and 1-methylnaphtalene) were used for negative ion formation of nitro group-based explosives: trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN). Presence of dopants in the sample results in multiple growth of ion yield at laser intensities lower than 2 × 107 W/cm². Limits of detection with dopant-assisted laser ionization (4.7 × 10^-16 g/cm³ for RDX and 9.8 × 10^-15 g/cm³ for PETN) show up to 2-fold improvement compared with no dopant case. Results propose a way to further improve sensitivity of detectors and reduce manufacturing costs by lowering requirements to laser pulse energy and using cheaper lasers.