A wet oxidation method for the compound‐specific determination of stable carbon isotopes (δ13C) of organic acids in the gas and aerosol phase, as well as of water‐soluble organic carbon (WSOC), is presented. Sampling of the organic acids was done using a wet effluent diffusion denuder/aerosol collector (WEDD/AC) coupled to an ion chromatography (IC) system. The method allows for compound‐specific stable carbon isotope analysis by collecting different fractions of organic acids at the end of the IC system using a fraction collector. δ13C analyses of organic acids were conducted by oxidizing the organic acids with sodium persulfate at a temperature of 100°C and determining the δ13C value of the resulting carbon dioxide (CO2) with an isotope ratio mass spectrometer. In addition, analysis of δ13C of the WSOC was performed for particulate carbon collected on aerosol filters. The WSOC was extracted from the filters using ultrapure water (MQ water), and the dissolved organic carbon was oxidized to CO2 using the oxidation method. The wet oxidation method has an accuracy of 0.5‰ with a precision of ±0.4‰ and provides a quantitative result for organic carbon with a detection limit of 150 ng of carbon. Copyright © 2006 John Wiley & Sons, Ltd.