The plots show deoxygenation of the broth, either by sparging with nitrogen or, if the culture consumes oxygen, by stopping the air flow. The dissolved oxygen concentration
drops during this period. Air is then pumped into the broth at a constant flow rate and the increase in
is monitored as a function of time. The oxygen concentration must remain above
, the critical oxygen concentration, when oxygen becomes the limiting substrate of cellular activity .
The electrode concentration is given by :
is the measured dissolved oxygen concentration and
is the electrode time constant.
For more information, including the effect of the transfer coefficient, consult the references.
 P. M. Doran, Bioprocess Engineering Principles
, Boston: Elsevier, 1995.
 I. J. Dunn, E. Heinzle, J. Ingham and J. E. Přenosil, Biological Reaction Engineering
, 2nd ed., Weinheim, Germany: VCH Verlagsgesellschaft mbH, 2003.