Surface-Assisted Laser Desorption/Ionization of Trinitrotoluene on Porous Silicon under Ambient Conditions

Abstract

Desorption/ionization on silicon (DIOS) is widely used in modern mass spectrometry for obtaining ions of various organic substances. The high efficiency of DIOS suggests that it may be a promising method in ion-mobility spectrometry (IMS) using gas-phase ion separation. The influence of laser wavelength and intensity on DIOS of trinitrotoluene (TNT) molecules under ambient conditions has been studied. If laser with a wavelength of 266 or 355 nm is used, TNT molecules predominantly form (TNT – H)− negative ions. Their formation has been found to result from laser-induced proton transfer from TNT molecules to the porous silicon (pSi) surface, rather than gas-phase ion–molecule reactions. The dependence of the yield of (TNT – H)− ions on the laser intensity has been analyzed. The ion yield curve has been demonstrated to fit the Arrhenius function at laser intensity lower than ∼2.5×107 W/cm2. Experiments have shown that the desorption/ionization of TNT molecules is not a purely thermal process. The results demonstrate that DIOS can be widely used in the IMS technology.