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06/2024 – Handling Polarographic Dissolved Oxygen (DO) Sensors: A Comprehensive Guide

DO measurement

Polarographic dissolved oxygen (DO) sensors are essential tools in various fields, including biotechnology, environmental monitoring, and water treatment. These sensors measure the concentration of dissolved oxygen in liquids, providing critical data for process control and quality assurance. Proper handling and maintenance of polarographic DO sensors are crucial for accurate and reliable measurements. This article outlines key steps and best practices for managing these sensors effectively.

Understanding Polarographic DO Sensors

Polarographic DO sensors operate on the principle of electrochemistry. They consist of a cathode (usually made of platinum or gold) and an anode (often silver or silver chloride) immersed in an electrolyte solution and separated from the sample by a gas-permeable membrane. When a voltage is applied, oxygen diffuses through the membrane and is reduced at the cathode, generating a current proportional to the oxygen concentration.

Steps for Effective Handling of Polarographic DO Sensors

  1. Initial Setup and Polarization
    • Sensor Connection: Connect the DO sensor to the appropriate controller or meter according to the manufacturer’s instructions. Ensure all connections are secure to avoid signal interference.
    • Polarization: Before using a new sensor or after prolonged storage, it must undergo polarization. This process involves applying a voltage to the sensor, allowing it to stabilize. Typically, polarization can take between 6 to 24 hours. Follow the manufacturer’s guidelines for the specific polarization time required.
  2. Calibration
    • Zero Calibration (0% Oxygen): Perform this calibration in an oxygen-free environment. This can be achieved by using a zero-oxygen solution or nitrogen gas. Ensure the sensor reads close to zero nA, indicating no oxygen presence.
    • Span Calibration (100% Oxygen): Calibrate the sensor in an environment with known oxygen concentration, usually air (20.9% oxygen). The sensor should provide a stable reading, typically in the range of 40 nA to 100 nA, depending on the sensor model and conditions.
  3. Maintenance
    • Regular Calibration: Regularly calibrate the sensor to ensure accurate measurements. Frequency depends on usage conditions but should generally be done before each measurement series or at least once a week.
    • Membrane and Electrolyte Replacement: Periodically inspect and replace the membrane and electrolyte solution. A damaged membrane or depleted electrolyte can lead to erroneous readings.
    • Cleaning: Clean the sensor regularly to remove any biofouling or debris. Use appropriate cleaning solutions recommended by the manufacturer to avoid damaging the sensor components.
  4. Operational Tips
    • Temperature Compensation: Ensure the sensor is equipped with temperature compensation, as oxygen solubility varies with temperature. Many modern sensors include automatic temperature compensation.
    • Sample Handling: Avoid bubbles in the sample, as they can cause fluctuations in oxygen readings. Stir or mix the sample gently to ensure homogeneity.
    • Storage: When not in use, store the sensor in a protective cap filled with a storage solution or in an appropriate dry place. Follow the manufacturer’s recommendations for long-term storage.
  5. Troubleshooting
    • Unstable Readings: If the sensor provides unstable or fluctuating readings, check for air bubbles under the membrane, proper sensor polarization, and adequate calibration.
    • Low or No Signal: Ensure the sensor is properly polarized and connected. Check the membrane and electrolyte for any signs of damage or depletion.
    • Slow Response Time: A slow sensor response can indicate membrane fouling or aging. Cleaning or replacing the membrane can resolve this issue.


Handling polarographic DO sensors with care and precision is essential for obtaining reliable data in any application involving dissolved oxygen measurement. By following proper setup, calibration, maintenance, and troubleshooting steps, you can ensure that your polarographic DO sensor provides accurate and consistent results. Regular attention to these details will extend the life of your sensor and enhance the quality of your measurements, ultimately contributing to the success of your operations.

For further information or specific guidelines, always refer to the manufacturer’s manual and support resources.