Patent ID: 6940083

Claim:
A stable isotope measurement method for spectrometrically analyzing an isotopic gas by introducing a gas specimen containing a plurality of component gases into a cell, measuring intensities of light transmitted therethrough at wavelengths suitable for the respective component gases, and processing data of the light intensities to determine a concentration ratio between the component gases, the component gases being carbon dioxide 12 CO 2 and carbon dioxide 13 CO 2 , the method comprising: a first step of introducing the gas specimen into the cell and into a gas injector which is communicated with the cell; a second step of injecting the gas specimen by the gas injector in a predetermined amount in the cell and pressurizing the gas specimen in the cell; a third step of determining absorbances of light transmitted therethrough at the wavelengths suitable for the respective component gases; and a fourth step of determining a concentration ratio between the component gases in the gas specimen on the basis of a calibration curve prepared through measurement on pressurized gas samples each containing the component gases in known concentrations.