Ocean Optics OOISensors - Manual (Page 53)

3: Oxygen Sensors
Samples should be maintained at a constant (+/-3 ° C*) temperature. If this is not practical, calibrate the
Fiber Optic Sensors System by using the temperature compensation features and measuring temperature
and oxygen concurrently. To monitor the temperature of the sensing environment and compensate for
temperature fluctuations, temperature electrodes can now be used in conjunction with the oxygen probe.
(Optional thermistor and K-type thermocouple accessories are available.) OOISensors Software corrects
for changes in data due to temperature fluctuations.
Note
Although Ocean Optics’ miniature spectrometers are extremely sensitive, the spectrometer cannot
detect temperature fluctuations +/-3
° C.
Scattering Media
Note
This section is relevant only if there is no overcoat applied to the oxygen probe.
Florescence emissions from the ruthenium complex propagate in all directions. In clear media, only those
emissions propagating toward the fiber within the acceptance angle of the probe are detected. If the probe
tip is held near a reflecting surface, or immersed in a highly scattering media, the fluorescence signal will
increase. The increase will be proportional for both the intensity of the fluorescence at a pressure of
oxygen and the intensity of fluorescence at zero pressure of oxygen, but will not affect the Stern-Volmer
constant. For this reason, it is necessary to measure the intensity of fluorescence at zero pressure of
oxygen in the sample. Furthermore, if you are measuring oxygen in highly scattering media, then the
standards you use for your calibration procedure should be in the same media as your sample for the most
accurate results.
Samples to Use
If you are using the probe in gases, N
2
can be used for the low value (0%) and either air (20.9%) or O
2
(100%) can be used for the high value.
If you are using the probe in liquid media, it may be difficult to prepare standards. Sodium hydrosulfite
dissolved in aqueous media consumes O
2
rapidly. You can use this to prepare a 0% concentration. Air-
saturated values for various solvents and salt solutions can be found in textbooks.
Note
Bubbling standardized gasses through the sample is an option but, depending on your setup, may
take more than 24 hours to reach equilibrium
FOXY-AL300-000-02-0207 43