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Working principle and application of fermentation dissolved oxygen electrode
Date: 2025-06-23Read: 3
The fermentation dissolved oxygen electrode is the core monitoring device for the fermentation process, and its working principle is mainly divided into two categories: polarographic and optical. Each has specific application scenarios in the fermentation industry:
1、 Working principle
1. Polarographic dissolved oxygen electrode
Oxygen reduction reaction: A polarization voltage of 0.6-0.8V is applied to the electrode surface, and dissolved oxygen passes through the polytetrafluoroethylene film. A reduction reaction (O ₂+2H ₂ O+4e ⁻ → 4OH ⁻) occurs at the precious metal cathode (such as platinum), while an oxidation reaction (4Ag+4Cl ⁻ → 4AgCl+4e ⁻) occurs at the anode (such as silver/silver chloride), forming a current circuit.
Correlation between current and oxygen concentration: According to Faraday's law, the diffusion current intensity is proportional to the partial pressure of dissolved oxygen, and the oxygen concentration is converted by detecting the current intensity.
Temperature compensation: Built in thermistor real-time corrects the effect of temperature on oxygen diffusion rate and solubility (error can exceed 1%/℃).
2. Optical dissolved oxygen electrode
Fluorescence quenching principle: Blue light excites the fluorescent substance inside the sensor to emit red light, and the collision between dissolved oxygen and fluorescent molecules causes the intensity of the red light to decay (quenching effect). The oxygen concentration is calculated by detecting the degree of red light decay.
No need for polarization and electrolyte: no electrochemical reaction, avoiding electrode polarization time and electrolyte maintenance requirements.
2、 Application features
1. Fermentation process monitoring
Real time online tracking of dissolved oxygen dynamics, such as a significant decrease in dissolved oxygen (DO) values during the logarithmic growth phase of Escherichia coli, followed by a rebound with bacterial aging in the later stages; Pichia pastoris needs to maintain>20% DO to ensure metabolic efficiency.
Stirring operation enhances electrode response accuracy by increasing oxygen diffusion.
2. Maintenance and reliability
The polarographic formula requires regular replacement of the oxygen permeable membrane and electrolyte, as membrane contamination or damage can cause data drift; Optical type only requires cleaning the fluorescent cap, with low maintenance costs.
The optical method has strong anti-interference ability (resistant to H ₂ S and pH fluctuations), while the stability of the polarographic method is insufficient for measuring trace amounts of oxygen.
3. Scene adaptability
The mature application of polarography in industrial fermentation tanks (such as METTLER TOLEDO electrodes) can withstand high temperatures up to 130 ℃.
Optical type is suitable for long-term continuous monitoring and complex water quality environments (such as sulfide fermentation broth).