Detection of Chemical Compositions of Ultrafine Nanoparticles by a Vacuum Ultraviolet Photoionization Nucleation Aerosol Mass Spectrometer

A vacuum ultraviolet photoionization nucleation aerosol mass spectrometer (VUVPI-AMS) was developed for detection of chemical compositions of ultrafine nanoparticles with size of less than 100 nm. A commercial nano-scanning mobility particle sizer (Nano-SMPS) was employed for size-selection of ultrafine nanoparticles, as well as the size distribution was measured. A special aerodynamic lens was designed to transfer and focus the ultrafine nanoparticles into the vacuum. On arriving on the hot surface of the heater, the ultrafine nanoparticles were vaporized and changed into gas-phase molecules, which were then softly photoionized at their ionization energy thresholds by the VUV photons emitted from a commercial 10.6 eV krypton discharge lamp. A home-made orthogonal acceleration reflectron time-of-flight mass analyzer was adopted to measure the mass of ions. As representative examples, the dioctyl phthalate (DOP) ultrafine nanoparticles and the nucleation nanoparticles from the ozonolysis reaction of α-pinene were measured and their chemical compositions were obtained with molecular information.