Species measurements in the beam of an ionic liquid ferrofluid electrospray source

Abstract

An ionic liquid ferrofluid (ILFF) using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-NTf2) as the carrier liquid was emitted from the peak formed via the Rosensweig instability and the electrospray beam was measured using quadrupole and TOF mass spectrometry. The Rosensweig instability peak source (RIPS) was found to operate in three stable emission current modes: transient-emission, lowcurrent, and high-current. Both quadrupole and linear TOF mass spectra for the final two modes were collected, and revealed that the charged-particle species within the electrospray beam varied between the two emission current modes. No correlation between the magnetic field strength and the collected mass spectra was measured. Mass flow measurements using a quartz crystal microbalance revealed that the RIPS only operated at a high mass flow rate of 3-5 ng/s during the startup transient-emission mode and otherwise ran at mass flow rates of 0.03-0.3 ng/s indicating the absence of droplet species during the majority of emission. The RIPS quadrupole mass spectra were compared to a pure ionic liquid needle source quadrupole spectra and it was discovered that multiple species exist in the ILFF electrospray that are attributed to fragments respective ion species, with some species partially comprised of fragments from the polymer used for steric stabilization of the nanoparticles; specifically the block that comprises the stabilization group, poly(N,N-dimethylacrylamide), and the end functionalizing group, CH3CHCOOH.