Abstract: A method and apparatus for measuring the amount of carbon and other organics in an aqueous solution is disclosed. A novel multistage reactor employs ultraviolet radiation to promote oxidation of a test sample. Oxygen and an oxidizing agent such as sodium persulfate are introduced into the solution prior to irradiation. The mixture is brought into direct contact with an ultraviolet lamp in each stage of the reactor. The design of the multistage reactor permits the desired chemical reaction to be optimized over interferring reactions.An inorganic carbon scrubber assembly is also disclosed for operation in a total organic carbon mode.