Polarographic oxygen sensor

From Bioblast

high-resolution terminology - matching measurements at high-resolution

Polarographic oxygen sensor


Polarographic oxygen sensors (POS) are operated with a polarization voltage between the cathode and anode, connected by an electrolyte. Cathode, anode and electrolyte are separated from the analyte by an oxygen-permeable membrane. Oxygen is reduced at the cathode such that the local oxygen concentration is maintained at zero, and diffuses along the concentration gradient from the stirred medium to the cathode, resulting in a linear calibration between oxygen partial pressure and electric current [Amp] (amperometric mode of operation). The OroboPOS is the POS applied in the Oroboros O2k.

Abbreviation: POS

Reference: OroboPOS

MitoPedia O2k and high-resolution respirometry: O2k hardware 

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From nM to mM O2 - a million-fold dynamic range: The dynamic range of oxygen measurement spans from air saturation (about 200 µM) to the normoxic intracellular range (10-30 µM) and severe hypoxia (<0.1 µM), but also to hyperoxia (oxygen saturation: c. 1 mM). In measurements of cell respiration in conjunction with the Titration-Injection microPump TIP2k, allow accurate steady-state measurement of oxgen levels and respiration with resolution of better than ±1 nM O2.
OroboPOS lifespan: As long as the quality control parameters are within the recommended range, the OroboPOS has no limited period of usage.
OroboPOS sensor head.jpg


OroboPOS are protected in a transparent perspex vial screwed onto a blue POM base, with the OroboPOS-Membrane Ring arrested on the POS shaft between the POM base and the thicker part of the POS head which holds an O-ring\Viton\8x1 mm.

POS service and membrane mounting

» O2k-Manual for OroboPOS service
» OroboPOS-Service Kit

Anode treatment by ammonia

The anode of the POS consists of a solid silver ring coated with silver/silver chloride. The AgCl coating will grow during use. A typical contamination is the formation of AgO. AgO is removed by the ammonia treatment during sensor service, however, part of the AgCl layer is removed in the process. Defects in the AgCl layer are restored by running the O2k for a few hours (or overnight) after sensor service and by continued use.

Delayed and slow response of the sensor

A slow POS has a long response time, responding to a change of oxygen partial pressure very slowly. The sensor response time can be most conveniently checked by the stirrer test.
A slow oxygen sensor cannot be used for kinetic studies, and may require prolonged periods of measurement at steady states. Individual POS have different response times, which change after sensor service. A slow response can be improved by:
  1. Sensor service and application of a new membrane. After sensor service, the POS needs some time in operation to stabilize, which may be a few or several hours (overnight). During this stabilization time, the oxygraph has to be running. After a sensor has been used and the seal tip has been removed from the sensor it is normal to see many small bubbles. This does not indicate that there was a problem while the sensor was actually in use.
  2. Theoretically a prolonged response time of a POS could be due to a hardware problem, which cannot be solved by intensive sensor service repeated several times. You may choose to ship the defective POS for special service to our workshop. We cannot predict, however, if such a special service will be successful.
  3. If not successful, the POS has to be replaced.

Sensor service by Oroboros

We offer a sensor service in our workshop. This is essentially the same that you can do on your own. The main advantage of the sensor service in our workshop is the presence of a very experienced and very patient team, carrying out many iterations of NH3 cleaning. Running the O2k overnight may be required to stabilize a newly serviced OroboPOS.

POS calibration and SOP

» Air calibration
» Zero calibration
» MiPNet06.03 POS-calibration-SOP
» Oxygen sensor test

Keywords: Oxygen signal


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  • Baglivo E, Cardoso LHD, Cecatto C, Gnaiger E (2022) Statistical analysis of instrumental reproducibility as internal quality control in high-resolution respirometry. Bioenerg Commun 2022.8. https://doi.org/10.26124/bec:2022-0008
  • Gnaiger E, Forstner H, eds (1983) Polarographic Oxygen Sensors. Aquatic and Physiological Applications. Springer, Berlin, Heidelberg, New York:370 pp. - »Bioblast link«
  • Gnaiger E (2001) Bioenergetics at low oxygen: dependence of respiration and phosphorylation on oxygen and adenosine diphosphate supply. Respir Physiol 128:277-97. - »Bioblast link«
  • Gnaiger E (2008) Polarographic oxygen sensors, the oxygraph and high-resolution respirometry to assess mitochondrial function. In: Mitochondrial Dysfunction in Drug-Induced Toxicity (Dykens JA, Will Y, eds) John Wiley:327-52. - »Bioblast link«

MitoPedia O2k and high-resolution respirometry: O2k hardware 

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