Electromembrane ion sources are considered as potential techniques for direct mass spectrometric sampling from ambient conditions. Interfacing of a time-of-flight mass spectrometer by means of a poly(ethylene terephthalate) track membrane requires investigation of the thermally activated processes involved. In this study, we directly attempt substantiating an activation-like performance of such track membrane-mediated interfaces. A number of KCl/glycerol solution samples were tested. A wide range of fixed, externally applied, potential drops was covered. For the charge extraction processes studied, we observe and discuss an activation term, exp(-ΔF/kBT), with a free-energy barrier ΔF = ΔF0 - ΔFΦ. The potential drop-dependent ΔFΦ, was found to be sensitive to the varying salt concentration.