Abstract <p>In this paper, we studied surface ionization under nonstationary conditions to estimate radicals formed during ionization of polyatomic molecules by the voltage modulation method. In the case of dissociative surface ionization of organic compounds, the ionization potential can conveniently be estimated based on an independently determined surface ionization coefficient. Experiments were conducted to study the kinetic properties of dissociative surface ionization and thermal desorption of nitrogen-containing polyatomic molecules, including imipramine, amitriptyline, novocaine, lidocaine, and tetraethylammonium chloride by the voltage modulation method. We determined the ionization potential of radicals from these compounds during nonstationary surface ionization by the voltage modulation method through calculation of the surface ionization coefficient β, which relied on measurements of the ion current from oscillograms recorded as the ionizing voltage varied at constant temperature.</p>