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 method for NO and NO(2) detection at the ultratrace level. Atmospheric pressure laser ionization (APLI), recently introduced by our group, is used to detect both compounds at low Darts per billion by volume (pptv) mixing ratios. APLI is based on resonance-enhanced multiphoton ionization mass spectrometry. Two-color pump-probe experiments employing a single excimer pumped dye laser combination allow for the ultrasensitive measurement of NO and NO(2) 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. NO(2) is ionized after double resonant excitation of the A (2)B(1) and 3p sigma manifolds in a (1 + 1' + 1(()'())) process using 431.65 + 308 mm. The selectivity of the NO measurement exceeds 2000 with respect to NO(2) and N(2)O(5). For NO(2), a selectivity of >3000 with respect to N(2)O(5) and organic nitrates is observed. The current APLI detection limit of NO and NO(2) is 0.5 and 5 pptv, respectively, with a 20-s integration time.