AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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Probing Reaction Rates in Single Aerosol Droplets Using a Branched Quadrupole Trap
GRAZIA ROVELLI, Michael Jacobs, Kevin Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 34 Working Group: Aerosol Chemistry
Abstract The acceleration of chemical reactions in aerosol particles has been observed in droplets generated by electrospray ionization and characterized with mass spectrometry (ESI-MS, Yan et al. (2016)). It is still unclear what are the main contributing factors to this phenomenon (e.g. high surface-to-volume ratios in droplets, local pH inhomogeneity, surficial charge, increased reagents concentration due to rapid solvent evaporation; Lee et al. (2015)) and what is the contribution of gas-phase reactivity in ESI-MS experiments (Jacobs et al. (2019)).
Jacobs et al. (2017) developed a branched quadrupole trap where two individual charged droplets of different chemical composition (each containing one reagent) can be merged on-demand to initiate a chemical reaction. The detection of reaction products with mass spectrometry or by measuring an increase in fluorescence due to the formation of fluorescent products (or its quenching caused by the consumption of a fluorescent reagent) allows to characterize the reaction kinetics in single aerosol droplets while reliably isolating the sole aerosol condensed phase reactivity.
The aim of this work is to determine what is the role of high surface-to-volume ratios in the enhancement of reaction rates within aerosol droplets using a branched quadrupole trap. The kinetics of the reaction between o-phtalaldehyde and alanine was studied as a function of the merged droplet size (from ~50 µm to ~1 µm in radius), by measuring the increase in fluorescence signal from the composite droplet as the fluorescent isoindole product is formed.
[1] Lee, J. K., et al. (2015). Q. Rev. Biophys., 48(4), 437–444. [2] Jacobs, et al. (2017). Anal. Chem., 89(22), 12511–12519. [3] Jacobs, et al. (2019). J. Am. Soc. Mass Spectrom., 30(2), 339–343. [4] Yan, X., et al. (2016). Angew. Chem. Int. Ed., 55(42), 12960–12972.