Laser analysis of the 13C/12C isotope ratio in CO2 in exhaled air

Tunable diode lasers (TDLs) are applied to the diagnostics of gastroenterological diseases using respiratory tests and preparations enriched with the stable ¹³C isotope. This method of the analysis of the ¹³C/¹²C isotope ratio in CO₂ in exhaled air is based on the selective measurement of the resonance absorption at the vibrational – rotational structure of ¹²CO₂ and ¹³CO₂. The CO₂ transmission spectra in the region of 4.35 μm were measured with a PbEuSe double-heterostructure TDL. The accuracy of carbon isotope ratio measurements in CO₂ of exhaled air performed with the TDL was ~0.5%. The data of clinical tests of the developed laser-based analyser are presented.