Multispecies breath analysis faster than a single respiratory cycle by optical-feedback cavity-enhanced absorption spectroscopy.

We demonstrate a first application, of optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS) to breath analysis in a medical environment. Noninvasive monitoring of trace species in exhaled air was performed simultaneous to spirometric measurements on patients at Bichat Hospital (Paris). The high selectivity of the OF-CEAS spectrometer and a time response of 0.3 s (limited by sample flow rate) allowed following the evolution of carbon monoxide and methane concentrations during individual respiratory cycles, and resolving variations among different ventilatory patterns. The minimum detectable absorption on this time scale is about 3 x 10(-10) cm(-1). At the working wavelength of the instrument (2.326 microm), this translates to concentration detection limits of approximately 1 ppbv (45 picomolar, or approximately 1.25 microg/m(3)) for CO and 25 ppbv for CH(4), well below concentration values found in exhaled air. This same instrument is also able to provide measurement of NH(3) concentrations with a detection limit of approximately 10 ppbv; however, at present, memory effects do not allow its measurement on fast time scales.