A method and apparatus for automated determining of the chemical oxygen demand of a liquid sample, comprising steps as follows: mixing the liquid sample with sulfuric acid; introducing a carrier gas, especially air, into the liquid sample-sulfuric acid mixture; adding an oxidizing agent to the liquid sample-sulfuric acid mixture to form a reaction mixture; heating (especially under reflux conditions) the reaction mixture at the boiling temperature of the reaction mixture for a predetermined time period; photometrically determining consumption of an oxidizing agent in the reaction mixture; and ascertaining therefrom the chemical oxygen demand of the liquid sample, wherein all steps are automatedly performed in an analytical system with the assistance of an evaluating and control unit.