A compact instrument that implements for the first time a method for analyzing substances, in which laser desorption of analyzed molecules and laser ionization of an air sample are combined with the ion mobility increment spectroscopy, is described. Pulse radiation of the fourth harmonic of a portable (2.6 kg) GSGG : Cr 3+ : Nd 3+ laser (λ = 266 nm) is used. The detection limit of the developed laser desorption spec trometer of the ion mobility increment is 40 pg for trinitrotoluene (TNT), and the linear dynamic range for TNT is 0.1-20.0 ng. The results from detection of nitro compounds are presented: trinitrotoluene, cyclotri methylene trinitramine (RDX), and octogen (HMX). It is shown that laser desorption of nitro compounds from a metal is accompanied by their decomposition on the surface and emission of fragments. An ion signal is obtained for nitro compounds that were ionized outside the spectrometer.
A new optical multipass scheme for laser field asymmetric ion mobility spectrometry (FAIMS) has been proposed and implemented. The scheme and the gas-analyzer system developed include both intracavity multiphoton laser ionization and FAIMS detection of the analyte. The computation and experimental results show multifold growth of the laser intensity in the FAIMS ion source, as well as the amplitude of ion signal. The gas phase detection threshold achieved is estimated to be 10−14 to 10–15 g cm−3. Further development of the proposed approach is discussed.
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