Field assessment of a new membrane-free microelectrode dissolved oxygen sensor for water column profiling

This article reports on the field trials of a membrane-free amperometric microelectrode dissolved oxygen sensor, which were performed during oceanographic cruise D279 of RRS Discovery. The sensor was used to obtain full depth oxygen profiles while mounted on a wire-operated CTD (conductivity, temperature, depth) instrument. A stable performance was achieved by carefully designed electrochemical cleaning conditions of the sensing platinum microdisk cathode. The flow issues inherent to moving probes were resolved by a novel stop-flow cell fitted with a pumping system for sample exchange and flow control. The details of the sensor operation, calibration, and construction, including the flow control system, are described. The sensor response is validated by calibration and by an analytical approach that yields oxygen data directly from the current readings. The accuracy of the microelectrode response is critically assessed using Winkler titrations on bottle samples taken during the relevant sensor deployments. The results lead to the conclusion that due to high accuracy, fast response time, and lack of membrane-related problems the device is particularly suitable for moving probes and high spatial resolution water column oxygen profiling.