Method for spectrometrically measuring isotopic gas and apparatus thereof

A method for spectrometrically measuring an isotopic gas by introducing a gaseous test sample containing a plurality of component gases including 12CO2 and 13CO2 into a cell, measuring intensity of light transmitted through the gaseous test sample at wavelengths suitable for the respective component gases, and processing data of the light intensity to determine concentrations of the component gases in the gaseous test sample, the method comprising:

• a first step of introducing the gaseous test sample into the cell and measuring absorbances of the respective component gases in the gaseous test sample;
• a second step of preliminarily determining concentrations of the component gases in the gaseous test sample on the basis of calibration curves prepared by using data obtained by measuring gaseous samples respectively containing the component gases in known concentrations within a predetermined range;
• and a third step of preparing new calibration curves by using some of the data within limited ranges around the concentrations of the component gases in the gaseous test sample preliminarily determined in the second step, and determining concentrations of the component gases in the gaseous test sample by using the calibration curves thus prepared.

A method for spectrometrically measuring an isotopic gas by introducing a gaseous test sample containing 12CO2 and 13CO2 as component gases into a cell, measuring absorbances of light transmitted through the gaseous test sample at wavelengths suitable for the respective component gases, and determining concentrations of the respective component gases on the basis of calibration curves prepared by measuring gaseous samples respectively containing the component gases in known concentrations, the method comprising:

• measuring two gaseous test samples obtained from one body and, if a concentration of 12CO2 in one of the two gaseous test samples is higher than a concentration of 12CO2 in the other gaseous test sample, diluting said one gaseous test sample to a 12CO2 concentration level equivalent to that of the other gaseous test sample, and then determining 13CO2/12CO2 concentration ratios in the respective gaseous test samples.

An apparatus for spectrometrically measuring an isotopic gas which is adapted to determine concentrations of a plurality of component gases in a gaseous test sample by introducing the gaseous test sample into a cell, then measuring intensity of light transmitted through the gaseous test sample at wavelengths suitable for the respective component gases and processing data of the light intensity, comprising:

• means for positioning the cell receiving the gaseous test sample introduced therein in the light path between a light source and a photoreceptor;
• a reference cell filled with a reference gas having no absorption at the wavelengths for measurement is disposed in a portion of the light path not occupied by the cell;
• and gas flow generating means for constantly passing the reference gas through the reference cell at a constant flow rate.

An apparatus for spectrometrically measuring an isotopic gas which is adapted to determine concentrations of a plurality of component gases in a gaseous test sample by introducing the gaseous test sample into two cells, then measuring intensity of light transmitted through the gaseous test sample at wavelengths suitable for the respective component gases and processing data of the light intensity, comprising:

• means for orienting the two cells for receiving the gaseous test sample introduced therein in parallel along light paths between a light source and a photoreceptor, the two cells having different lengths;
• a reference cell filled with a reference gas having no absorption at the wavelengths for measurement disposed between a shorter one of the two cells and the photoreceptor or between the light source and the shorter cell;
• and gas flow generating means for constantly passing the reference gas through the reference cell at a constant flow rate.