A method and device are provided for dynamic flash combustion reaction connected with gas chromatography for the elemental analysis of C H N S O in an automatic elemental analyzer. A combustion reactor is provided with a sampling device and an oxygen feed line. Controlled volumes of oxygen are admitted with the oxygen feed line into the combustion reactor depending on the sample for the complete combustion thereof. A pneumatic circuit is provided, in which the oxygen feed line converges and the pneumatic circuit creates a continuous flow of a carrier gas that is able to carry the oxygen to the reactor and the gases of the combustion through the reactor, then through a gas chromatographic analyzer, and after their separation, into a thermal conductivity detector. An electronic apparatus with a data processor is provided for controlling the process systems. The difference in the pressure of the gas upstream and downstream of a restrictor or restriction is determined. The electronic pressure regulator or flow regulator of the reference carrier gas and at least one carrier gas outlet valve, which is also used as purging, is inserted on this carrier gas reference line.