An improved apparatus and method for the automatic determination of total organic carbon in aqueous media. The invention comprises two sample injection valves, two reaction chambers, one for converting all carbon (both organic and inorganic) in the sample to carbon dioxide, the other for converting only the inorganic carbon to carbon dioxide, a methanizer for converting the formed carbon dioxide to methane and a flame ionization detector for measuring the quantity of the methane produced which corresponds to the total and the inorganic carbon content of the sample, the difference between these two values being the organic carbon content.