An IT-TOF mass spectrometer for the analysis of organic aerosol

An ion trap time-of-flight (IT-TOF) mass spectrometer has been developed for online analysis of organic aerosol. Airborne particles are focused through an aerodynamic lens assembly and deposited onto a stainless steel collection probe inserted through a hole in the ring electrode of an ion trap. The collected sample is desorbed and ionized with a pulsed 355-nm Nd:YAG laser beam within the ion trap cavity. Ions are collisionally cooled to the center of the trap prior to extraction into a reflectron time-of-flight mass analyzer. Relative to a previous version of the instrument without an ion trap, incorporation of the ion trap increases the sensitivity and resolution of ions that are formed directly at the probe surface and permits post-ionization with electrons to be performed. Online analysis of perylene and C60 test aerosols were performed by one-step laser desorption ionization (LDI). Online analysis of secondary organic aerosol (SOA) from α-pinene ozonolysis was performed by laser desorption–electron ionization (LD–EI). Matrix-assisted laser desorption ionization (MALDI) was also performed, and the molecular ion signal was enhanced with a dynamic RF trapping method.