Laser-induced fluorescence spectroscopy of 14N18O and its application to breath analysis.

Laser-induced fluorescence (LIF) spectroscopy is an efficient tool for the detection of low nitric oxide (NO) concentrations down to the parts per trillion (ppt) range. The isotopic selectivity of this method provides a broad potential of applications. Whereas (14)N(16)O and (15)N(16)O have been described extensively this is not the case for the (14)N(18)O isotopologue. A (1+1) resonance enhanced multiphoton excitation time-of-flight mass spectrometer has been used for the simultaneous detection of (14)N(16)O, (15)N(16)O and (14)N(18)O isotopologues. Regions with single (14)N(18)O transitions have been studied in more detail by the LIF device. Electronic excitation of the A-X transition in the UV provides fluorescence which is monitored around 247 nm from A(2)Sigma(+)(v'=0)-->X(2)Pi(Omega)(v''=2). This transition has been used for an isotope specific online detection of (14)N(18)O from exhaled air. The detection limit for (14)N(18)O is 7.3+/-1.8 ppt. With respect to (18)O-labelled drugs and amino acids this denotes a novel extension to NO research.