High precision measurements of the 13CO2/12CO2 isotope ratio at atmospheric pressure in human breath using a 2 μm diode laser

A special technique is developed to measure the 13CO2/12CO2 isotope ratio in human breath at atmospheric pressure with a 2 μm tunable diode laser. The procedure used to process the pressure-broadened spectra obtained and calculating the isotope ratio is based on a multidimensional linear regression of the spectra using simulated 13CO2, 12CO2, and H2O spectra. This technique allows the measurement of the δ-value for isotopic ratios with a precision of 0.07‰ within a data acquisition time of 3 min and a long-term reproducibility of 0.2‰.

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