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Talk:Oxygen flux in open O2k-Chamber

From Bioblast



Mario Fasching

Template:Technical service


In an open chamber situation the liquid phase in the chamber is in equilibrium with the atmosphere. All oxygen consumed by the POS is immediately replaced from the atmosphere. The oxygen signal therefore has to be constant and the non-background corrected oxygen flux (= first time derivative of the oxygen signal, called "O2 slope uncorr." in DatLab) has to be zero. The background corrected flux is meaningless for the open chamber situation. This is because the background corrected flux corrects for consumption of oxygen by the sensor and diffusion into and out of the closed chamber. Since neither of the latter have any effect on the zero flux in the open chamber situation, an incorrect flux will result when background correction is applied. Only Layouts that display "O2 slope" uncorrected are suitable for assessing the O2 flux at open chamber. Such Layouts are:

  • 01 Calibration Exp Gr3-Temp
  • 02 Background Experiment
  • 04 Flux per Volume uncorrected
  • Z Trouble Shooting

The observation of a zero flux with an open chamber is an important performance parameter. It indicates that thermal stability has been reached. Therefore no experiment should be started before a zero oxygen flux has been reached with an open chamber. The suggested criterion for "zero flux" is a flux between -1 pmol/(s ml) and + 1 pmol (s ml).


Problem:

  • The uncorrected slope does not reach the interval +/- 1 pmol/(s ml) even after a prolonged time.

Solutions:

  • The open chamber situation may not be ideal. Remove the stoppers completely and create a new gas phase as described in open chamber.
  • The slope is always calculated from the calibrated O2 signal. Check the POS calibration
  • Observe the Raw signal and check if it is in the expected range
  • If the raw signal is unstable, and thereby creating an apparent O2 flux, follow the instructions for Locating a problem.

See also:

POS calibration MiPNet12.08

O2 Flux analysis MiPNet12.09