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10.4 Temperature
The InPro 6880 i sensor contains a RTD and the tem-
perature is compensated automatically.
10.5 Dependence on flow
The optical Oxygen sensor InPro 6880 i shows a stron-
gly reduced flowdependence compared to the ampero-
metric sensors.
The reason is that the optical sensor does 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
ned 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, the oxygen concentration can be de-
termined by means of the electrode. This applies at
constant temperature and with dilute aqueous soluti-
ons 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)
InPro 6880 i
52 206 256
InPro 6880 i Series O
permeability of the membrane – but not
2
solubility in the solutions. The oxygen con-
2
/l (CL) cannot therefore be determi-
2
• a
2
2
2
Solubility at 20 °C (68 °F)
and 760 mm Hg
9.2 mg O
/l
2
2 mg O
/l
2
21.9 mg O
/l
2
© 09/07 Mettler-Toledo AG
Printed in Switzerland
Sensor 12 mm
).
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