DESIGN OF LIQUID-VERTICAL-BAR-LIQUID ELECTROCHEMICAL-CELLS

Electrochemical cell designs for liquid\liquid studies have been brief ly summarised. Experiments using reference Luggin capillaries mounted on ball and socket joints showed that the lateral separation between t he Luggin tips on either side of the liquid\liquid interface had a neg ligible effect upon the solution resistance. However, the vertical sep aration, especially of the Luggin tip on the organic side, did have a significant effect upon the uncompensated solution resistance. Even sm all amounts of uncompensated solution resistance will lead to signific ant peak separations which might be mistaken for kinetic limitations. Correct compensation of the solution resistance is essential for liqui d\liquid systems. In many cell designs for liquid\liquid systems, the counter electrode for the organic phase is actually in an aqueous solu tion which is connected to the organic phase by a porous glass frit. T he electrical connection between the two phases then relies upon the t ransfer of a common ion. If the size of the glass frit is too small, t he transfer of the common ion can be limited and this in turn will lea d to current limitations in the overall cell currents. This results in a characteristic 'clipping' of the current in a cyclic voltammogram, which cannot be traced to faults in the electronic instrumentation. To avoid this problem, the frit must be at least twice the size of the i nterface. A new electrochemical cell design for liquid\liquid studies which does not possess a Luggin capillary for the organic phase is rep orted. This Luggin-less cell will exhibit lower impedances for the ref erence electrode arm than the more conventional reference arms involvi ng Luggin capillaries. (C) 1997 Elsevier Science S.A.