Glycerol-wetted track membranes (poly(ethylene terephthalate)) are suitable for interfacing between a typical TOF chamber (held at an operational pressure of less than 10-6 Torr) and an ambient pressure analyte. Solute concentration aspects of track membrane mediated electrostatic introduction of negative charged species into TOF mass spectrometer were investigated. Glycerol solutions of KCl, KBr, NH4I, and Na2S were used. High-field charge extraction conditions were routinely maintained between the liquid samples (held at ambient pressure) and a grounded grid collector. The latter was positioned just nearby the vacuum facing side of such membranes. Upon establishing a steady-state charge extraction regime, the collector currents were monitored and recorded at various solute concentration levels. Nonlinear, solute concentration dependent, collector currents were observed and found to correspond to our theoretical treatment. Our findings are accounted for and in support of a special, evaporation limited, mechanism for the track membrane mediated high-field extraction of cluster ions.