The main compartment of the titration cell contains the anode solution plus the analyte. The anode solution consists of an alcohol (ROH), a base (B), sulfur dioxide () and KI. Typical alcohols that may be used include ethanol, diethylene glycol monoethyl ether, or methanol, sometimes referred to as Karl Fischer grade. A common base is imidazole.
The titration cell also consists of a smaller compartment with a cathode immersed in the anode solution of the main compartment. The two compartments are separated by an ion-permeable membrane.
The Pt anode generates  from the KI when current is provided through the electric circuit. The net reaction as shown below is oxidation of  by . One mole of  is consumed for each mole of . In other words, 2 moles of electrons are consumed per mole of water.
The end point is detected most commonly by a bipotentiometric titration method. A second pair of Pt electrodes is immersed in the anode solution. The detector circuit maintains a constant current between the two detector electrodes during titration. Prior to the equivalence point, the solution contains  but little . At the equivalence point, excess  appears and an abrupt voltage drop marks the end point. The amount of charge needed to generate I and reach the end point can then be used to calculate the amount of water in the original sample.