A REMPI Method for the Ultrasensitive Detection of NO and NO₂Using Atmospheric Pressure Laser Ionization Mass Spectrometry

Abstract

We report on the development of a quasi-simultaneous highly selective method for NO and NO2 detection at the ultratrace level. Atmospheric pressure laser ionization (APLI), recently introduced by our group, is used to detect both compounds at low parts per trillion 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 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 2sigma+ (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 A2B1 and 3psigma manifolds in a (1 + 1' + 1(')) process using 431.65 + 308 nm. The selectivity of the NO measurement exceeds 2,000 with respect to NO2 and N2O5. For NO2, a selectivity of>3,000 with respect to N2O5 and organic nitrates is observed. The current APLI detection limit of NO and NO2 is 0.5 and 5 pptv, respectively, with a 20-s integration time.

Development of medium pressure laser ionization, MPLI. Description of the MPLI ion source

“…The 50 ϫ 20 ϫ 20 (L ϫ W ϫ H) cm 3 body was constructed as one piece from aluminum to be dimensionally compatible with a Pfeiffer TC 600 (Pfeiffer, Asslar, Germany) three-port turbo drag pump backed by a Pfeiffer Duo 10 roughing pump. The two high vacuum ports of the pump were directly connected to the differential pumping chamber and analyzer region of the main housing.…”

“…The analyte mixing ratios and total gas flow were controlled with an MKS up/downstream flow control system as has been shown elsewhere [3].…”

“…Utilizing a novel pulsed valve capable of time-resolved sampling at atmospheric pressure coupled to a variety of time-of-flight (TOF) mass spectrometers, several atmospherically relevant trace gases have been selectively and sensitively detected in the laboratory. This technique was recently introduced by our group as "Atmospheric Pressure Laser Ionization Mass Spectrometry" (APLI-MS) [2,3].…”

Conductive carbon filled polymeric electrodes: Novel ion optical elements for time-of-flight mass spectrometers

“…The vapor was diluted with He. The analyte gases were diluted using MKS mass flow controllers and a down-stream pressure regulator, as described in detail in [6].…”

“…In an effort to create increasingly compact TOF instruments, our research group has focused on novel approaches to instrument design and laser ionization techniques [5][6][7]. With this in mind, we have initiated research that is concerned with the production of "ideal" electrostatic fields.…”