The rate of hydrogen–deuterium exchange (HDX) in aqueous droplets of phenethylamine
has been determined with submillisecond temporal resolution by mass spectrometry using
nanoelectrospray ionization with a theta-capillary. The average speed of the microdroplets is
measured using microparticle image velocimetry. The droplet travel time is varied from 20 to
320 μs by changing the distance between the emitter and the heated inlet to the mass
spectrometer and the voltage applied to the emitter source. The droplets were found to …