A REMPI method for the ultrasensitive detection of NO and NO2 using atmospheric pressure laser ionization mass spectrometry

We report on the development of a quasi-simultaneous highly selective metho d for NO and NO2 detection at the ultratrace level. Atmospheric pressure la ser ionization (APLI), recently introduced by our group, is used to detect both compounds at low Darts per billion by volume (pptv) mixing ratios. APL I is based on resonance-enhanced multiphoton ionization mass spectrometry. Two-color pump-probe experiments employing a single excimer pumped dye lase r combination allow for the ultrasensitive measurement of NO and NO2 within a narrow range of maximum pumping efficiency of the laser dye Coumarin 120 . NO is detected via excitation of the long-lived A (2)Sigma (+) (nu' = 1) level at 215.36 nm and subsequently ionized with 308-nm radiation provided by the excimer pump laser. NO2 is ionized after double resonant excitation of the A B-2(1) and 3p sigma manifolds in a (1 + 1' + 1(()'())) process usi ng 431.65 + 308 mm. The selectivity of the NO measurement exceeds 2000 with respect to NO2 and N2O5. For NO2, a selectivity of >3000 with respect to N 2O5 and organic nitrates is observed. The current APLI detection limit of N O and NO2 is 0.5 and 5 pptv, respectively, with a 20-s integration time.