A laser desorption ion-mobility increment spectrometer for detection of ultralow concentrations of nitro compounds

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 ionmobility increment spectroscopy, is described. Pulse radiation of the fourth harmonic of a portable (2.6 kg) GSGG: Cr³⁺: Nd³⁺ laser (λ = 266 nm) is used. The detection limit of the developed laser desorption spectrometer 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, cyclotrimethylene 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.