Real-time Detection and Tandem Mass Spectrometry of Secondary Organic Aerosols with a Quadrupole Ion Trap

An aerosol quadrupole ion trap mass spectrometer is reported that is sensitive, has unique capabilities to perform chemical ionization, is operated in real-time, and is able to perform tandem mass spectrometry. The instrument samples particles with an aerodynamic lens and volatilizes them within the heated ion trap electrode assembly. Analyte molecules are ionized within the ion trap by proton transfer from reagent ions, and resultant fragmentation is reduced compared to vacuum UV photoionization. Particle concentrations can be detected linearly over two orders of magnitude and as low as 5 μg/m3. To demonstrate the real-time analysis capability of the instrument, secondary organic aerosol particles were produced by reaction of 100 ppb α-pinene and 200 ppb ozone in an aerosol bag and observed in real-time to monitor the progress of the reaction. Pinic acid and pinonic acid are two of the many components of the secondary aerosol mixture that form and gradually decrease in concentration. Individual concentrations are calculated using pinic acid as an internal standard and vary from 4-36 ppb. The identities of analyte ions from both compounds are confirmed by tandem mass spectrometry in real-time.