Patent ID: 7749436

Claim:
In an isotope gas analysis in which gas to be measured or an expired breath of a human being containing, as gas components, carbon dioxide 13 CO 2 and carbon dioxide 12 CO 2 , is introduced into a cell, and the intensities of transmitted lights having wavelengths suitable for measurement of the respective gas components, are measured and then data-processed to measure the concentration of the carbon dioxide 13 CO 2 , a gas injection amount determining method comprising the steps of: filling the cell with the air at an atmospheric pressure; operating a gas injection device so as to suck the air of a predetermined volume Va, the gas injection device being arranged to inject the gas to be measured into the cell; transferring the air stored in the gas injection device into the cell to pressurize the cell inside, and measuring the cell inside pressure P; and subtracting the cell volume Vc from the product obtained by multiplying the sum V 0 of the volume Va and the cell volume Vc, by the ratio P 0 /P in which P 0 is the target pressure of the gas to be measured in isotope gas analysis measurement, thus determining the one-time gas injection amount of the gas injection device.