Studying Chemistry in Micro-compartments by Separating Droplet Generation from Ionization

Area of Science:

• Chemical Kinetics
• Physical Chemistry
• Analytical Chemistry

Background:

• Reactions within micron-sized compartments, like droplets, exhibit accelerated rates and altered mechanisms compared to bulk solutions.
• Electrospray ionization mass spectrometry (ESI-MS) is commonly used to study droplet reaction kinetics, but droplet charging and evaporation complicate analysis.
• Gas-phase ion-molecule and clustering reactions in ESI-MS can interfere with the interpretation of droplet-confined reactions.

Purpose of the Study:

• To decouple droplet generation from ionization to investigate the role of gas-phase chemistry in reaction acceleration.
• To compare the reactivity of sugar phosphate formation in droplets versus the gas phase.
• To assess the potential for gas-phase processes to complicate the interpretation of ESI-MS data for droplet reactions.

Main Methods:

• Separation of droplet generation from the ionization source.
• Utilizing electrospray ionization mass spectrometry (ESI-MS) for product ion detection.
• Measuring the formation of sugar phosphates from phosphoric acid and simple sugars.

Main Results:

• The same product ions previously attributed to in-droplet reactions were observed both with and without compartmentalization.
• Gas-phase processes occurring in the ionization region can significantly complicate the quantification and interpretation of accelerated droplet reactions.
• Gas-phase reactions were demonstrated to be a significant, potentially dominant, pathway for sugar phosphate formation.

Conclusions:

• Gas-phase reactions can be a major contributor to observed rate accelerations in ESI-MS studies of droplet chemistry.
• The interpretation of accelerated reactions in droplets using ESI-MS may require careful consideration of non-droplet-related processes.
• Future research should incorporate methods to distinguish between in-droplet and gas-phase reaction contributions.