High precision measurements of the -(13)CO_2/-(12)CO_2 isotope ratio at atmospheric pressure in human breath using a 2 μm diode laser

摘要

A special technique is developed to measure the -(13)CO_2/-(12)CO_2 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 cal culating the isotope ratio is based on a multidimensional lin ear regression of the spectra using simulated -(13)CO2, -(12)CO2, 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 re-producibility of 0.2‰.