Determination of kinetic characteristics of thermal desorption of cocaine by mass-spectrometric method of surface ionization

Abstract

The adsorption and surface ionization of cocaine molecules C₁₇H₂₁NO₄ (M: 303 Da) on the surface of oxidized tungsten was studied using the non-stationary voltage modulation method in a high-vacuum mass spectrometric setup employing a “black chamber,” all the walls of which are cooled with liquid nitrogen. The activation energy Е⁺ and Е⁰ of thermal desorption were determined, as well as pre-exponential factors in the continuity equation for the radicals C₁₂H₈ON ⁺ and C₁₂H₈ON (m/z 182) during the dissociation of cocaine molecules with a break (C–C₁) _β bonds with the formation of desorbing radicals by surface ionization on the surface of oxidized tungsten W_xO_y. The results of determining the coefficient of surface ionization, the heat of sublimation, and assessing the ionization potentials of these radicals are presented, and also determined from thermal desorption spectra of the activation energy of thermal desorption of the resulting ions in the air atmosphere.