Dissolved Oxygen

Dissolved oxygen is one of the most important indicators in a fermentation or bioreactor process. It determines the potential for growth. The measurement of dissolved oxygen is made by a sterilizable probe inserted directly into the aqueous solution of the reactor. Two principles of operation are used for this measurement: the first is an electrochemical reaction while the second employs an amperometric (polarographic) principle.

The electrochemical approach uses a sterilizable stainless steel probe with a cell face constructed of a material which will enable oxygen to permeate across it and enter the electrochemical chamber which contains two electrodes of dissimilar reactants (forming the anode and cathode) immersed in a basic aqueous solution (Fig. 2). The entering oxygen initiates an oxidation reduction reaction which in turn produces an EMF which is amplified into a signal representing the concentration of oxygen in the solution.

Figure 2. Sterilizable polarimetric dissolved oxygen probe. (Courtesy of Ingold Electrodes, Inc., Wilmington, Mass.)

In the amperometric (polarographic) approach, oxygen again permeates a diffusion barrier and encounters an electrochemical cell immersed in basic aqueous solution. A potential difference of approximately 1.3 V is maintained between the anode and cathode. As the oxygen encounters the cathode, an electrochemical reaction occurs:

The hydroxyl ion then travels to the anode where it completes the electrochemical reaction process:

The concentration of oxygen is directly proportional to the amount of current passed through the cell.

Was this article helpful?

0 0

Post a comment