Two approaches to sample controlled thermal analysis (SCTA) used preparatively were contrasted using the air activation of a nutshell derived carbon. The rate of reaction, corresponding to the level of evolved carbon dioxide, was monitored using a quadrupole mass spectrometer and controlled via software using a feedback loop. In the first approach, control of the rate was achieved via temperature under a constant concentration of oxygen in nitrogen, while in the second the reactant gas concentration (oxygen/nitrogen ratio) was changed while the furnace was held isothermally. Due to the exothermic nature of the carbon-oxygen reaction, temperature control of the activation process at high reaction rates was difficult and produced oscillatory behaviour, while good control of the process could be achieved using the gas concentration method at higher reaction rates. By using oxygen rather than the more usual CO2 or H2O activation at 800-1000 degrees C, the reaction takes place at 200-300 degrees C with a consequent significant saving in energy costs. Published by Elsevier Science B.V.