Abstract: This invention provides devices for the measurement of total organic carbon content in water samples. The device has a microfluidic sample cell with a sample channel for receiving a water sample wherein the water sample can be irradiated with UV radiation to oxidize organics to CO2. The sample channel is sufficiently thin in the region irradiated to allow very rapid substantial mineralization of the organics in the sample. A photocatalyst, such as TiO2 or platinized TiO2 can be employed to speed sample oxidation. Substantial mineralization of a sample can be achieved in less than about 30 seconds, significantly decreasing the time required for making a TOC measurement. CO2 generated by sample oxidation can be detected and/or quantitated by various methods, particularly by conductivity measurements or by infrared methods.