Headspace oxygen linearity

Fyhr et al. [201] reviewed several commercially available oxygen analyzers intended for the analysis of oxygen in the headspace of vials. However, preliminary validation revealed insufficient reproducibility and linearity. The authors developed headspace analysis systems. Sample volumes down to about 2.5 ml could be used without significant errors. Sample recovery was in the range 100-102%. It was necessary to measure the head-space pressure and volume in order to be able to present the assay in partial oxygen pressure or in millimoles of oxygen. Up to 40 vials per hour could be analyzed using this technique. 

Fig. 5. Dependence of paclitaxel production on headspace gas concentrations of ethylene, carbon dioxide and oxygen according to the linear regression model...

Data from the stoppered culture tests was also used to determine the effect of declining 02 concentration on the rate of metabolism of the cells. The specific 02 consumption rate was determined to depend linearly upon the 02 concentration throughout the range of headspace concentrations measured (0-31 %). This seems to contradict the experience of other researchers [31-33, 50], who report saturation kinetics in plant cell cultures whenever 02 concentration exceeded 4-5% (gas phase). In the stoppered culture tests, at the same time 02 concentration declined, C02 and C2H4 concentrations increased. Other unidentified compounds may also have been produced. The declining rate of metabolism observed may have been caused by conditions other than declining oxygen. 

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