ICL-based TDLAS sensor for real-time breath gas analysis of carbon monoxide isotopes

We present a compact sensor for carbon monoxide (CO) in air and exhaled breath based on a room temperature interband cascade laser (ICL) operating at 4.69 µm, a lowvolume circular multipass cell and wavelength modulation absorption spectroscopy.A fringelimited (1σ) sensitivity of 6.5 × 10 -8 cm -1 Hz -1/2 and a detection limit of 9 ± 5 ppbv at 0.07 s acquisition time are achieved, which constitutes a 25-fold improvement compared to direct absorption spectroscopy.Integration over 10 s increases the precision to 0.6 ppbv.The setup also allows measuring the stable isotope 13 CO in breath.We demonstrate quantification of indoor air CO and real-time detection of CO expirograms from healthy non-smokers and a healthy smoker before and after smoking.Isotope ratio analysis indicates depletion of 13 CO in breath compared to natural abundance.