文摘
With the availability of broadly tunable external cavity quantum cascade lasers (EC-QCLs), particularly bright mid-infrared (MIR; 3鈥?0 渭m) light sources are available offering high spectral brightness along with an analytically relevant spectral tuning range of >2 渭m. Accurate isotope ratio determination of 12CO2 and 13CO2 in exhaled breath is of critical importance in the field of breath analysis, which may be addressed via measurements in the MIR spectral regime. Here, we combine for the first time an EC-QCL tunable across the 12CO2/13CO2 spectral band with a miniaturized hollow waveguide gas cell for quantitatively determining the 12CO2/13CO2 ratio within the exhaled breath of mice. Due to partially overlapping spectral features, these studies are augmented by appropriate multivariate data evaluation and calibration techniques based on partial least-squares regression along with optimized data preprocessing. Highly accurate determinations of the isotope ratio within breath samples collected from a mouse intensive care unit validated via hyphenated gas chromatography鈥搈ass spectrometry confirm the viability of IR-HWG-EC-QCL sensing techniques for isotope-selective exhaled breath analysis.