Temperature; Dependence On Flow; Oxygen Partial Pressure - Oxygen Concentration - Mettler Toledo InPro 6000 Serie Instructions D'utilisation

InPro 6000 Series Optical O

10.4 Temperature

The optical oxygen sensor contains a RTD and the tem-
perature is compensated automatically.

10.5 Dependence on flow

The optical oxygen sensors show a strongly reduced flow
dependence compared to the amperometric sensors.
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
on the O
centration in mg O
mined 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 so-
lution:
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)
© 08 / 12 Mettler-Toledo AG
Printed in Switzerland
Sensors 12 mm
2
permeability of the membrane – but not
2
solubility in the solutions. The oxygen con-
2
/ L (CL) cannot therefore be deter-
2
• a
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
InPro 6000 optical O
).
2
sensors
2
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