We developed a system that links a thermal desorption oven for aerosol filter samples to an isotope ratio mass spectrometer (IRMS) via a combustion interface. Organic compounds are desorbed from the filter sample in He at 7 temperature steps between 100 and 400 degrees C and subsequently oxidized to CO2, which is analyzed for delta C-13. We tested the system for isotopic fractionation, reproducibility and linearity using organic test compounds and aerosol filter samples. An oxalic acid standard with known delta C-13 value shows no isotopic fractionation when it is desorbed at temperatures well above its melting point. When organic acids are heated at a temperature close to their melting point only a fraction of the compound (10-80%) evaporates which shows depleted delta C-13 values at this temperature step. At the next higher temperature step, when the rest of the compound is desorbed, delta C-13 values are enriched. This effect is stronger for compounds with a lower molecular weight than for compounds with a higher molecular weight. In ambient samples this should only have a moderate effect on the overall delta C-13 value, since hundreds of different compounds are desorbed at each temperature step. Choosing different values for temperature steps does not strongly change the delta C-13 values for ambient aerosol filter samples. For typical ambient samples the reproducibility lies below +/-0.3 parts per thousand for oven temperatures below 200 degrees C and below +/-0.5 parts per thousand for oven temperatures above 200 degrees C. Tests with oxalic acid and ambient filter samples show that the IRMS is linear for peak areas in the operational range of 1-20 V s. (C) 2013 Elsevier Ltd. All rights reserved.