Construction and testing of a durable platinum wire Eh electrode for in situ redox measurements in the subsurface

We have developed a rugged, durable platinum wire Eh electrode for applicat ion in subsurface environments. The electrode design is described in detail and its performance under aerobic and anaerobic steady-state and transient conditions is assessed. The electrode consists of a 0.5-mm-diameter platin um wire (99.99% purity) cast in a glass fiber-reinforced epoxy jacket. The construction allowed installation through direct insertion into sandy media to depths up to several meters. Data collection was through connection to a datalogger with high impedance input; data points were collected every 10 seconds and averaged and stored once an hour. The electrodes functioned in situ for periods of more than three years and gave reliable readings durin g oxic, anoxic, and transitional conditions. Performance testing and examin ation of electrodes recovered after three years in situ indicated that they were not impacted by corrosion, dissolution, or poisoning.