A novel method for the measurement of oxygen mass transfer rates in small-scale vessels

A novel method for the measurement of the volumetric oxygen transfer coefficient, kLa, using the catechol-2,3-dioxygenase (XylE) bio-oxidation of catechol yielding 2-hydroxymuconic semialdehyde (2-HS), has been developed for small-scale systems. This method was kinetically characterized and validated by comparison to other established techniques. The bio-oxidation rate was found to be zero order over a catechol concentration from 2 to 7 mM l−1. When the enzyme concentration was in excess and the bio-oxidation rate was mass transfer limited, indicated by a percent DOT of zero, the oxygen transfer rate was determined from the linear increase in product concentration. The method was validated in a 2 l stirred tank vessel equipped with a DOT probe and connected to a gas mass spectrometer. The novel method yielded similar kLa values when compared to the dynamic gassing out method under the same conditions. The applicability of this novel method for small-scale devices was demonstrated by measuring kLa values of up to 150 h−1 in shaken microplates with a working volume of only 200 μl.