Oxygen electrode dynamics

KLADYN, KLAFIT and ELECTFIT - Dynamic Oxygen Electrode Method for KLa System... 

Ruchti, G., Dunn, I.J. and Bourne J.R. (1981). Comparison of Dynamic Oxygen Electrode Methods for the Measurement of KLa, Biotechnol. Bioeng. 13, 277. 

Transient Holdup Profiles in an Agitated Extractor 459 Homogeneous Free-Radical Polymerisation 310 Batch Reactor Hydrolysis of Acetic Anhydride 247 Continuous Bioreactor with Inhibitory Substrate 543 Dynamic Oxygen Electrode 462... 

Merchuk et al. [276] investigated the dynamics of oxygen electrodes when analyzing mass transfer, and they reported whether and when an instantaneous response occurs. A semiempirical description of diffusion coefficients was provided by Ju and Ho [198]. Bacillus subtilis cultures change the product concentration ratio between acetoin and butanediol rapidly in the range of p02 =80-90 ppb [286]. This fact could be used for the characterization of the oxygen transport capabilities of bioreactors. 

Ruchti G, Dunn IJ Bourne JR (1981) Comparison of dynamic oxygen electrode methods for the measurement of Kip. Biotechnology and Bioengineering 23 277-290. 

The term dynamic response method refers to methods in which oxygen electrodes in the liquid respond rapidly to changes in the composition of the gas phase. They are mainly employed in fermentation technology. The problems which arise either depend upon the response behavior of the electrodes or upon assumptions made with regard to the mixing of the gas cushion and the liquid. Many publications refer to the special features of the measuring technique [71, 97], the sources of error [265] and modeling [106, 372]. 

Comparison of Dynamic Oxygen Electrode Methods for the Measurement of KLa, Biotechnol. Bioeng., 13, 277. 

Models Considering Membrane Diffusion and Time Delay. Lopez et al. (2006) and Vardar and Lilly (1982) suggested that when the electrode dynamic response was first order with a time delay, the following model can be used to correct the dissolved oxygen concentration data ... 

Linek, V, and Sinkule, J. (1990), Comments on vaUdity of dynamic measuring methods of oxygen diffusion coefficients in fermentation media with polarographic oxygen electrodes, fi/ofechwoZogy and B/oengineen ng, 35(10) 1034-1041. 

Callus cultures were established with three olive (Olea europaea L.) varieties using a method reported previously (2). Volatiles were collected from the olive cultures (20g) using dynamic headspace sampling techniques described previously (3). Analysis of volatiles was performed using an Automatic Thermal Desorption System linked to a Perkin Elmer Autosystem GC. Lipoxygenase (LOX) activity of the cultures was assayed routinely using an oxygen electrode. 

As shown below, the influence of three quite distinct dynamic processes play a role in the overall measured oxygen concentration response curve. These are the processes of the dilution of nitrogen gas with air, the gas-liquid transfer, and the electrode response characteristic, respectively. Whether all of these processes need to be taken into account when calculating KLa can be seen by examining the mathematical model and making simulations. 

Response time. In the literature, response time is usually specified as the time taken for the electrode to reach > 90% of the output. Typical response times are around 30 sec. A fast response time is critical when one is measuring transient phenomena such as oxygen respiration rates in tissue or suspended cells and dynamic measurements of the volumetric mass transfer coefficient in bioreactors. 

Yttria stabilized zirconia formed by this reaction fills the air electrode pores. The dynamics of this CVD stage has been modeled by Carolan and Michaels [120], who observed that films produced in this manner penetrate the substrate no more than 2-3 pore diameters from the chloride face of the substrate. It has also been shown that the penetration depth is independent of water concentration. The second step of this method is the EVD step. Once pore closure is achieved, the reactants are not longer in contact. Electrochemical semipermeability related to the existence of small electronic conductivity and large gradient of oxygen partial pressure leads to oxygen transport from the steam side to the chloride side through the deposited electrolyte. The electrochemical reactions involved are ... 

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