Ion-Transfer Voltammetry at the Interface between Organic and Salt-Doped Ice Phases

Ions play critical roles in reactions of biological, environmental, and industrial importance under frozen conditions. Transfer voltammetry of tetramethylammonium (TMA) and K+ ions is measured at the interface between frozen aqueous NaCl and dichloroethane to give an insight into chemistry in frozen aqueous phases. The ion-transfer current of TMA initially increases as the temperature becomes lower from the freezing point, but the further decrease in temperature reduces the transfer current. The half-wave potential of the TMA transfer shows a negative shift when the liquid phase volume is smaller than 10% of the total volume of the frozen phase. Similarly, the half-wave potential of the facilitated transfer of K+ by crown ether complexation also becomes negative with decreasing temperature, due to the freeze concentration of K+ in the liquid phase.