Abstract: To reach higher precision is of critical importance in the application of gas chromatography to determine the amount of CO₂ in the atmosphere. As described in this paper, the velocity at which the gas sample is introduced is controlled using an Hg pressed intrument under normal temperature and pressure. The fluctuation in the pressure of the gas samples in the quantitative tube is decreased as well. As a consequence, the determination of the quantity of CO₂ is achieved to an accuracy of 10^-6.