Non-invasive and isotope-selective laser-induced fluorescence spectroscopy of nitric oxide in exhaled air

The detection of nitric oxide (NO) is of considerable medical interest. NO is involved in a multitude of mammal physiological processes, and various non-invasive concentration determination methods for NO have been developed during the last few years. Regarding time resolved metabolism behavior the quantitative determination of the (15)N(16)O-isotopologue in combination with (15)N-labeled drugs and amino acids is a central interest of current medical research. We apply laser-induced fluorescence (LIF) spectroscopy for isotope-selective detection of NO in various biological environments with a theoretical detection limit below 0.1 parts per trillion (ppt). Electronic excitation of the AX-transition in the UV provides fluorescence around 247 nm from [Formula: see text]. For an online measurement of human exhaled air, a respiratory mask has been constructed and integrated into our system. This paper gives an overview of the applied LIF device for non-invasive detection of NO originated from exhaled human air. The main advantages of this device compared to established methods are as follows: high sensitivity for NO concentrations in the ppt region, a high time resolution of 20 ms and isotopic selectivity to distinguish between (14)NO and (15)NO. Visualizations of single-exhalation profiles and long-time online measurements including the determination of absolute NO concentrations are presented and the influence of quenching gases present during the experiment is discussed. To our knowledge, we present for the first time time-resolved (15)NO online profiles of exhaled human air.