AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
A Quadrupole Electrodynamic Trap Coupled to Single Droplet Mass Spectrometry: A Tool to Study Aerosol Heterogeneous Reactivity
MEGAN WILLIS, Grazia Rovelli, Kevin Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 211 Working Group: Instrumentation and Methods
Abstract Trapping and levitation of single particles has become an important tool to investigate the physical and chemical properties of aerosol particles under controlled laboratory conditions. Particle levitation provides access to heterogeneous chemistry at atmospherically relevant conditions through reaction timescales of hours to days and, correspondingly lower oxidant concentrations compared to shorter reaction timescales. Chemical evolution in trapped particles can be followed using spectroscopic techniques; however, these approaches are not amenable to all atmospherically relevant chemical systems. We couple a linear quadrupole electrodynamic trap (QET) to single droplet mass spectrometry to probe the chemical evolution of the condensed phase due to heterogeneous reactions on populations of trapped droplets. The multi-compartment QET is housed in an environmentally controlled chamber and allows for continuous trapping of a droplet population (~10 – 100 droplets). Single droplets are transferred to a lower compartment for sizing using the Mie scattering pattern from illumination by a 532 nm laser introduced axially. Single droplets are subsequently ejected to the ionization region of an ambient pressure inlet mass spectrometer. We extend previous work using paper spray mass spectrometry coupled to a branched QET (Jacobs et al., 2017), to the use of electrospray ionization (ESI) and solvent-assisted inlet ionization (SAII). Our aim is to establish a reproducible and quantitative method for detecting organic compounds, and their reaction products, in single micron sized aqueous or pure component droplets. We explore the time resolution required to capture and quantify droplet events using ESI and SAII, and the sensitivity of these two approaches as a function of droplet size, concentration and charge. We develop the use of droplet internal standards inert to reaction with the chosen oxidant to improve the reproducibility of droplet detection. Finally, we study the ozonolysis of organic acid alkenes, and examine the interchangeability of reaction time and oxidant concentration.
Jacobs et al. (2017). Anal. Chem., 89(22), 12511–12519.