The methods specified are based on heating a portion of the test sample at a temperature of at least 1100 °C to 1200 °C in an oxygen atmosphere, passing the evolved oxidation products over a purification trap filled with manganese dioxide catalyst and silver permanganate catalyst (that oxidises CO to CO2), trapping the CO2, restoring the initial pH continuously by addition of hydroxyl ions either by potentiostatic titrimetry or by coulometry, or alternatively determining the CO2 by IR absorption and integration of the signal obtained. Is applicable to the determination of 5 µg to 500 µg of carbon.