A novel titration electrode for measuring the concentration of CO2 is described in which OH- is generated electrochemically and the time taken for the OH- to be titrated by the CO2 is measured. A theoretical description of the variation of pH with time is presented. The curve is shown to have two inflection points. The pH at the second point of inflection is close to 8. Hence the time to the second point of inflection is the titration time. Results from experiments with known quantities of OH- are shown to be in good agreement with the theory.