Amir Naqwi — MSP Corporation
Christopher Joseph Hogan — University of Minnesota
Deborah Gross — Carleton College, MN
Lin Li — MSP Corporation
Hongxu Duan — MSP Corporation
Siqin He — University of Minnesota
Category
General topics – Aerosols
Description
Photographs of aerosol electrospray ionization device in operation. (a) Electrostatic precipitation mode: aerosols charged with a corona charger are brought to a rod with opposite electrical potential, so they deposit on the tip of the rod electrostatically. (b) Electrospray ionization mode: An electrically conductive solvent, e.g. methanol with acetic acid, is brought to the tip of the rod for dissolving compounds from the captured particles. A high voltage, positive or negative, is applied to the tip of the rod for generation of the ions with the corresponding charges. These ions are drawn into Mass Spectrometer Inlet and analyzed for m/z ratio.
Chemical composition measurement of atmospheric aerosols is of considerable interest and has been facilitated by mass spectrometry. In this project, we are utilizing the soft ionization capability of electrospray ionization (ESI) to produce parent ions from molecules in aerosol particles. ESI is proven to enable the ionization of large organic compounds (up to several hundred kilo-Daltons) with minimal ion fragmentation, facilitating the analysis of a variety of organic species that are otherwise unmeasurable via mass spectrometry. The instrument being developed in this project, Aerosol Electrospray Mass Spectrometer (AEMS), automates the steps of transferring aerosol into liquid and generating charged droplets, without the need for a separate extraction step. Particles are charged and electrostatically precipitated on the tip of a rod, which is subsequently wetted with a solvent in order to dissolve compounds from the aerosol and ionize them using the electrospray ionization technique. As opposed to the conventional laboratory analysis using particulate matter collected on a filter/substrate, our approach enables rapid analysis and delivers results in near-real-time. Phase I efforts were focused on developing a device for collecting aerosols and releasing ions from them using the electrospray technique, i.e. a front-end device that would be compatible with common mass spectrometers. This device was proven with several compounds commonly found in atmospheric aerosols, including levoglucosan, levoglucosan mixed carbon nanoparticles, and secondary organic aerosol generated from α-pinene and toluene ozonolysis. We used a QSTAR XL quadrupole-time-of-flight mass spectrometer for its high mass resolution and high mass accuracy, as well as an LTQ Velos Pro ion trap mass spectrometer to utilize MSn capabilities and high sensitivity. Results of these measurements are presented and discussed.
