Cobalto-cobaltic oxide is used as the oxidizing agent in micro Dumas method for the analysis of refractory organic compounds. The permanent, oxidizing filling is only 4 cm long. The sample is mixed with the temporary filling in a capsule 7 cm in length, and the combustion is carried out at 700°, without introducing gaseous oxygen into the system. The combustion and the sweeping-out take 10-15 minutes. Satisfactory results have been obtained on heterocyclic compounds, polymers, aliphatic compounds with relatively long chain, compounds with condensed ring systems and angular methyl groups, as well as highly fluorinated compounds and polymers. With certain types of perfluoro-compounds such as perfluorobutyric acid and polymers such as polyacrylonitrile, the temperature of sample heater should be increased to 750° for satisfactory results.