Development of Hg-Au Microelectrode for Measuring O2, Mn2+, Fe2+ and S2− in Marine Sediment Pore Water

Hg-Au voltammetric microelectrodes were developed by electroplating mercury membrane onto Au microelectrodes. The Au electrode was constructed by sealing one end of a 100-μm diameter gold wire within a glass capillary using epoxy and attaching the other end to a silver wire for electrical contact using conductive epoxy. The silver wire was fastened to the top of the glass tube using epoxy again. The tip of the electrode was ground flat and smooth gradually from coarse to fine grain under a micropolisher. It was then washed in 1 M HNO3 solution and in deionized water under supersonic action. The electrode was electroplated with a layer of mercury within 0.1 M Hg(NO3)2/0.03 M HNO3 electrolyte at a potential of −0.10 V versus saturated calomel electrode (SCE) for 5 min. By adopting three-electrode cell and square wave voltammetry, Hg-Au microelectrode can measure dissolved oxygen, Mn2+, Fe2+ and sulfide during a single potential scan from −0.10V to −1.75V versus saturated calomel electrode (SCE). The experimental results indicated that the microelectrode had the sensitivity and detection limit of 0.16 nA μM−1, 6 μM for dissolved oxygen; 0.35 nA μM−1, 3 μM for Mn2+; 0.22 nA μM−1, 5 μM for Fe2+, and 34 nA μM−1, 0.03 μM for sulfide. It was found that the microelectrode exhibited good reproducibility with an error below 3% after measuring 15 sediment samples consecutively.