What does a Dissolved Oxygen Meter do?

The conventional measurement system of DO consists of a meter and a Clark-type  polarographic probe. The probe is the most important and delicate part of the system. The probe consists of a silver (Ag) anode wrapped with a platinum (Pt) wire that functions as a cathode. These are inserted into a protective cap filled with a potassium chloride (KCl) electrolyte solution. The cap ends in a PTFE membrane, a gas-permeable material that allows the passage of oxygen present in the solution, but not in the solution itself.

By applying a potential of 790mV, the oxygen present in the cell is reduced to hydroxide ions (OH^-) at the cathode, and silver chloride (AgCl) is deposited at the anode. This reaction provokes a current flux with intensity proprtional to the quantity of oxygen in the present sample. The meter converts the current into the corresponding concentration of oxygen.

It should be noted that the solubility of oxygen is dependent on many factor includes temperature, atmospheric pressure and salinity. Some of Hanna oxygen meters automatically compensate for these variables and ensure even greater accuracy.

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