Field Testing of a New Self-contained Fluorescence Oxygen Probe with a Fast Response Time for Continuous In-situ Monitoring

We report on the development of an optical dissolved oxygen (DO) probe with a 10 second response time. The DO concentration is determined by measuring the oxygen quenching of the phosphorescence from inorganic, metal-halide optical indicators. The sensor probe is completely self-contained within a compact (2cm x 2cm x 20cm) water-proof body which includes both the fluorescence spectrometer and optical sensing film. Input power and data communications occur via a USB cable. The probe outputs a temperature, pressure and salinity corrected measurement of DO. Our device is designed to operate outdoors in temperatures ranging from 10 to 35 °C, in an array of aqueous liquids of varying salinity, pH as well as organic and mineral contaminants. Calibration curves over DO concentrations of 0 to 10mg/l were obtained. The response of the sensor to a step change in oxygen concentration is <10sec. This response time will enable rapid oxygen depth profiling measurements.

We present field data from continuous outdoor deployments in the presence of aquatic organisms, during growth of bio-films on the sensing membrane and in high mineral content waters. Comparisons are presented with DO data obtained from local geological services. Our oxygen sensing probe is well suited for both depth profiling applications and continuous, in-situ monitoring in a diversity of aquatic environments.