Abstract: The invention relates to a process and detector for determining organic and inorganic chemical substances by chemiluminescence with ozone, the selectivity and specificness of the detector being a function of the degree of reactivity of the chemical substances with ozone in distinct temperature ranges. The chemiluminescence reaction takes place in the reaction chamber of the detector, in the absence of oxygen, and with thermal control. The detector comprises the following units: ozone generator, reaction chamber, discharge means for gases issuing from the reaction chamber, an optical system, a photomultiplier, amplifier data transformer and recorder.