Suppose we are growing the cells inside the reactor, we start with a fresh inoculum. How can we calculate the kLa inside the reactor, while changing the agitation rate (RPM). Ca anyone please reply to this question. I would be thankful.
Before describing some methods to measure the liquid phase mass transfer coefficient (hereafter referred to as kLa), it's worthwhile to state the governing equation as obtained by performing a mass balance on the dissolved oxygen:
dC/dt=OTR−OUR
where C stands for the dissolved oxygen concentration and OTR and OUR refer to the oxygen transfer rate and the oxygen rate respectively. If all the cells in the bioreactor are dead or there is no biomass present, the oxygen uptake rate, OUR, is equal to 0, and the governing equation reduces to:
dC/dt=kLa(C∗−C)
There are a large number of methods available to measure kLa which can be broadly classified into chemical and physical methods. I will briefly describe some of these here, first covering the chemical methods and then the physical ones.
Chemical methods C1. Sodium sulfite oxidation method C2. Carbon dioxide absorption method C3. Hydrazine oxidation method C4. Catechol bio-oxidation method C5. Glucose oxidase method C6. Krypton absorption method
Physical methods P1. Dynamic method P2. Dynamic gassing-out method P3. Dynamic pressure step method
C1. Sodium sulfite oxidation method
The most common chemical method involves oxidation of a sulfite solution (typically sodium sulfite) to sulfate, a reaction which is catalyzed by many metal ions or iodine. For our purposes here, the general reaction is adequately described by:
The progress of the reaction can be followed by titration with sodium thiosulphate or other appropriate methods and follows the differential equation:
−dCNa2SO3dt=2kLaC∗−dCNa2SO3dt=2kLaC∗
... and kLa can be easily evaluated.
In a variant of this method, the change in pH during the oxidation of sulfite to sulfate is tracked, either directly using a pH probe or indirectly using a pH-sensitive dye like bromothymol probe. Using these measurements, an estimate of kLa can also be obtained.
Hi Shiva,
Thank you for the reply. I want to know how can we exactly calculate the kLa while we vary the RPM inside the reactor while the cell culture is growing. I have found in the literature they use Dynamic gassing out method, but it has not been explained in detail, how do they use it. Do you have any information.
Regards,
Sohail
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