Temperature; Dependence On Flow; Oxygen Partial Pressure - Oxygen Concentration - Mettler Toledo InPro 6000 Bedienungsanleitung

InPro 6000 Series Optical O

10.4 Temperature

The optical oxygen sensor contains a RTD and the
temperature is compensated automatically.
10.5 Dependence on flow
The optical oxygen sensors show a strongly reduced
flow dependence compared to the amperometric sen-
sors.
The reason is that these optical sensors do not reduce
oxygen. No change in the oxygen concentration occurs
at the sensor.
10.6 Oxygen partial pressure – oxygen concentration
The sensor signal depends on the oxygen partial pres-
sure and the O
not on the O
concentration in mg O
determined directly with an electrode.
According to Henry's law the oxygen concentration is
proportional to its partial pressure (PO
CL = pO
a = solubility factor
If "a" is constant and known, the oxygen concentration
can be determined by means of the electrode. This ap-
plies at constant temperature and with dilute aqueous
solutions such as drinking-water.
The solubility factor is strongly influenced not only by
the temperature but also by the composition of the
solution:
Medium,
sat. with air
Water
4 mol/ L KCI
50 % Methanol-water
Although the solubilities vary widely, the oxygen elec-
trode gives the same reading in all three solutions.
Thus, determination of the oxygen concentration is
only possible with constant and known solubility
factors "a".
Solubility may be determined by a Winkler titration or
the method developed by Käppeli and Fiechter.
References
– W.M. Krebs, I.A. Haddad Develp. Ind. Microbio.,
13, 113 (1972)
– H. Bühler, W. Ingold GIT 20, 977 (1976)
– W.M. Krebs, MBAA Techn. Quart. 16, 176 (1975)
– D.P. Lucero, Ana. Chem. 40, 707 (1968)
© 01/ 2016 Mettler-Toledo GmbH InPro 6000 optical O
Printed in Switzerland
Sensors 12 mm
2
permeability of the membrane – but
2
solubility in the solutions. The oxygen
2
• a
2
/ L (CL) cannot therefore be
2
Solubility at 20 °C (68 °F)
and 1013 mbar (760 mm Hg)
9.2 mg O / L
2
2 mg O / L
2
21.9 mg O / L
2
).
2
sensors
2
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