How do you measure concentration of CO2?
The most direct way is to react it with a base, like sodium hydroxide.
Different types of analyzers are not available for rapid calculation of CO2 concentrations from different sources. These may be Infrared detectors, a variety of detectors on a gas chromatograph or mass spectrometers.
However, before those can be used, a standard value of carbon dioxide still needs to be established. The old, original chemical reaction methods remain reliable and accurate. A sample of CO2 is put in a calibrated volumetric vessel and NaOH solution is added to it. It reacts completely with all available CO2, so the volume difference in the vapor in the vessel is the original amount of CO2 present in the sample.
For more details, examples and procedures, look up ORSAT analysis.