A method and device are provided for flash dynamic combustion reaction connected with gas chromatography for the elemental analysis of C H N S O in an automatic elemental analyzer. A combustion reactor (11) is provided with a sampling device (10) and an oxygen metering (14) support line. Controlled volumes of oxygen are admitted with the oxygen metering support line into the combustion reactor depending on the sample for the complete combustion thereof. A pneumatic circuit (13) is provided, in which the oxygen feed line converges and 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 (12), and after their separation, into a heat-conductivity sensor. An electronic apparatus with a data processor (16) is provided for controlling the process systems. The difference in the pressure of the gas upstream and downstream of is 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 washing, is inserted on is carrier gas reference line.