AbstractA new tool for the measurement of TOC based on the heterogeneous photocatalysis activated by two different light sources has been planned. The instrument is constituted by a cell where the degradation occurs thanks to both the UV irradiation and the presence of a powered catalyst and by a measurement cell lodging CO2 gas permeable membrane electrode (detector), thermometer, inlet and outlet ways for the samples. One of the sources has a maximum emission at 254nm, while the other simulates the solar spectrum. A suspension (1 g/L) of titanium dioxide (Degussa P25) has been used to catalyse the process. A magnetic stirrer and a circulating pump avoid the deposition of the catalyst on the bottom of the reactor. The online measurement of produced CO2 was performed on 11 molecules (commercial names: Parachlorophenol, D‐Glucose, Acid Blue 29, Atraton, Aspirin, Dimethoate, Aldicarb sulfone, Hydroquinone, (R)‐Propranolol, Citric acid, Atrazine) to test the system efficiency. The experimental CO2 value was compared with the theoretical TOC value calculated by means of the structure's formula.