Since oxygen is involved in most of the biological and chemical processes in aquatic environments, it is a crucial parameter to measure. Oxygen can also be used as a tracer in oceanographic studies. Aanderaa revolutionized oceanographic oxygen monitoring/research with the introduction of oxygen Sensor in 2002. Applications range from shallow creeks to the deepest trenches, from tropical to in-ice/in-sediment measurements. More than 200 scientific papers have so far been published using these optodes, including publications on the oxygen sensor working principle. The oxygen sensor is designed to measure absolute oxygen concentration and % saturation. The sensor can be used from streams to deep sea, from fish farms to waste water and from polar ice areas to hydrothermal vents.
These sensors are based on the ability of selected substances to act as dynamic fluorescence quenchers. The fluorescent indicator is a special platinumporphyrin complex embedded in a gas permeable foil that is exposed to the surrounding water. This sensing foil is attached to a glass window providing optical access to the measuring system from inside a watertight housing. The sensing foil is excited by modulated blue light; the sensor measures the phase of the returned red light. For improved stability the sensor also performs a reference phase reading by use of a red LED that do not produce fluorescence in the foil. The sensor has an incorporated temperature thermistor which enables linearization and temperature compensation of the phase measurements to provide the absolute O2-concentration.
The lifetime-based luminescence quenching principle offers the following benefits:
- Response time <8 sec (63%)
- High accuracy
- Not stirring sensitive (it consumes no oxygen)
- Lower fouling sensitivity
- Measures absolute oxygen concentrations without repeated calibrations
- Better long-term stability
- Hot water monitoring
- Less affected by pressure
- Not sensitive to H2S
- Not freezing sensitive