On March 23, 2012 an in situ interlaboratory comparison measurement of dissolved oxygen concentration EstDO-2012 was carried out at the Testing Centre of University of Tartu. Altogether 13 participants from Estonia (different institutions), Germany (IO Warnemünde), France (IFREMER) and Finland (SYKE) took part in the intercomparison. The participants used amperometric and optical (fluorescence quenching) sensors.

There is a perception that measurement of dissolved oxygen concentration is simple. In reality it is not. Dissolved oxygen is an unstable analyte and its determination is affected by numerous uncertainty sources (a comprehensive overview of the uncertainty sources of amperometric dissolved oxygen sensors and ways of taking them into account is given in a recent review: Sensors 2010, 10, 4430-4455, open access). Therefore such comparisons between laboratories are essential for improving the quality of measurements made by laboratories.

In situ intercomparisons are organized in such a way that all participants gather in the same place and make measurements on the same object. The “object” in this case was a basin of water with carefully controlled dissolved oxygen content. The basin was immersed in a themostat for temperature control and the water was stirred because the readings of the amperometric sensors depend on stirring. The sensors of the participants were arranged concentrically to allow similar intensity of water movement in the vicinity of the sensors. Picture on the right shows the basin and the sensors.

Connected to the intercomparison was a demonstration of the primary semi-gravimetric micro Winkler titration method that has been developed at University of Tartu. This method offers very high accuracy and does not need calibration with water of known concentration of dissolved oxygen. More information can be found in a presentation Determination of dissolved oxygen – half-gravimetric Winkler given at the intercomparison.

The final report of the EstDO-2012 intercomparison is available from the Intercomparisons website of the UT Testing Centre.

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Organization of this intercomparison has been partly funded by the European Metrology Research Programme (EMRP), project ENV05 “Metrology for ocean salinity and acidity”. The EMRP is jointly funded by the EMRP participating countries within EURAMET
and the European Union.

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