CHARACTERIZATION AND APPLICATIONS OF A HG/AU PEEK MICROELECTRODE/FLOW-CELL SYSTEM FOR IN SITU ANALYSIS OF SURFACE AND GROUND WATER

One way to use voltammetry for environmental analysis is with a thin-film Hg/Au microelectrode encased in PEEK. This type of electrode was originally developed at the University of Delaware by G.W. Luther and colleagues. The electrode is composed of a Hg-plated 100 µm diameter gold wire imbedded in epoxy in a PEEK tubing body. The reference electrode and counter electrode are Ag/AgCl and platinum, respectively. These electrodes have been used for in situ measurements of dissolved oxygen, manganese, iron, sulfide, and other redox-sensitive species in suboxic water columns and at hydrothermal vents (Luther et al., Mar. Chem., In Press).

In this study, PEEK microelectrodes are used in conjunction with a minimal-volume flow cell. Sample flow through the flow cell is generated by a peristaltic pump. The microelectrode/flow cell system has potential applications for the monitoring of redox-sensitive chemical species and some trace metals in shallow wells and in surface waters. Preliminary experiments have been run to determine the effect of varying salinity on the electrode response for dissolved O₂, Mn²⁺ and HS^-. Electrodes were tested over a range from 0-35 salinity to simulate the range of salinities found in salt-marsh tidal creeks, estuaries and/or near-shore groundwaters. With the exception of a significant decrease in sensitivity for Mn²⁺ from 0 to 5 salinity, little to no salinity effects were observed for O₂, Mn²⁺ and sulfide. (Fe²⁺ is expected to behave similarly to Mn²⁺, due to the formation of chloro complexes with increasing salinity). In further studies, the PEEK electrode/flow cell system will be used to test the redox conditions and concentrations of chemical species in a salt-marsh tidal creek over a full tidal cycle. The system will also be integrated with a well-sampling system to study shallow submarine ground water discharge. The latter could be a contributor to episodic near-shore hypoxic conditions observed in Long Bay (NE South Carolina coast) during the summer.