Shaping electrospray plume with convergent sound beams.

Electrospray ionization (ESI) is one of the mainstream ionization techniques for mass spectrometry (MS) nowadays. Here, we present a new variant of ESI-MS setup, in which an electrospray emitter points to the mass spectrometer's orifice while the collimated sound (from one or four woofers) propagates orthogonally to the plume and MS inlet axis. First, we investigated deflection of electrospray microdroplets of different sizes by the sound waves using high-speed imaging. Low-frequency sound influences microdroplets of different sizes to a varied extent enabling partial separation. Second, we conducted a series of on-line experiments using a range of peptides, polymers, and amino acids. The influence of sound on microdroplet motion is more pronounced at higher amplitudes and lower frequencies of the signal used to generate the sound stream. Our findings provide a way to modulate electrospray process and can impact the application areas of electrospray including MS and materials science.