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.

In the past decade, due to a growing awareness of the importance of air quality and air pollution control, many diagnostic tools and techniques have been developed to detect and quantify the concentration of pollutants such as NO x , SO x , CO, and CO 2 . We present here an Incoherent Broad-Band Cavity-Enhanced Spectroscopy (IBB-CEAS) setup which uses a LED emitting around 625 nm for the simultaneous detection of NO 2 and NO 3 . The LED light transmitted through a high finesse optical cavity filled with a gas sample is detected by a low resolution spectrometer. After calibration of the spectrometer with a NO 2 reference sample, a linear multicomponent fit analysis of the absorption spectra allows for simultaneous measurements of NO 2 and NO 3 concentrations in a flow of ambient air. The optimal averaging time is found to be on the order of 400 s and appears to be limited by the drift of the spectrometer. At this averaging time the smallest detectable absorption is 2×10−10 cm −1 , which corresponds to detection limits of 600 pptv for NO 2 and 2 pptv for NO 3 . This compact and low cost instrument is a promising diagnostic tool for air quality control in urban environments.