Gold ultra-microelectrode arrays: Application to the steady-state voltammetry of hydroxide ion in aqueous solution

Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide ions and are shown to be analytical useful. Two types of ultra-microelectrode arrays are used; the first consist of 256 individual electrodes of 5 mu m in radius, 170 of which are electrochemically active in a cubic arrangement which are separated from their nearest neighbour by a distance of 100 mu m. The second array compromises 2597 electrodes of 2.5 mu m in radius and of which 1550 of which are electrochemically active in a hexagonal arrangement separated by the nearest neighbour by 55 mu m. Well defined voltammetric waves are found with peak currents proportional to the concentration of hydroxide ions in the range 50 mu M to 1 mM. Detection limits of 20 mu M using the 170 ultra-microelectrode and 10 mu M with the 1550 ultra-microelectrode array are shown to be possible but with a higher sensitivity of 4 mA M-1 observed using the 1550 ultra-microelectrode array compared to 1.2 mA M-1 with the 170 ultra-microelectrode array.