Universal Cone Angle of ac Electrosprays Due to Net Charge Entrainment

Abstract

The half-angle of an ac cone is shown to exhibit a universal (length-scale independent) asymptotic value of 12.6 degrees at high-permittivity ratio, which is quite distinct from the 49.3 degrees of dc Taylor cones. Our theory and experiments suggest that ac entrainment of low-mobility anions, generated by field-assisted ion dissociation, sustains a net charge at the ac cone. Mutual Coulombic repulsion between these free charges compensates the singular azimuthal capillary force and elongates the cone with an axial force that does not exist in dc cones.

High-frequency AC electrospray ionization source for mass spectrometry of biomolecules

“…As shown in Figure 1b, these AC cones, which have a half cone angle of ϳ11°and exhibit a continuous longitudinal growth in time are significantly different from static DC Taylor cones (with half cone angle ϳ49°), pulsating electrosprays [13], or low-frequency (Ͻ10 kHz) AC electrosprays [14] (Supplementary Material showing an AC cone of ethanol solvent at an applied AC potential of frequency 80 kHz and magnitude ϳ 5.5 kV (peak to peak) along with the preliminary sensitivity curve and positive mode mass spectra of cytochrome c, which can be found in the electronic version of this article). The formation of the AC cone is due to the difference in the mobility of liquid phase anions and cations that leads to a build up of the low mobility species in the cone because of insufficient time to relax onto the surface of the meniscus when the AC signal switches polarity-a condition induced when the inverse relaxation time scale is less than the high-frequency of AC signal [12]. This asymmetric effect leads to a net space charge in the cone from the accumulation of low-mobility ions, and the resulting Coulombic repulsion sustains the AC cone.…”

On the Principles of Printing Sub-micrometer 3D Structures from Dielectric-Liquid-Based Colloids

“…[ 14 ] Such highly focused cone jet (with associated small droplets) is observed for liquids with relatively high electrical conductivity, [ 15 ] or for dielectric liquids seeded with additives. [ 16 ] Recently, Stachewicz et al [ 17 ] extended this technique to perform on-demand, single-event electrospraybased printing using pulsed electric fi elds. Two very-important aspect of reliable fabrication of functional features and devices using printing techniques are the ability to control the deposit morphology and also the ability to form 3D structures; however, to the best of our knowledge, no previous work based on the electrospray technique has explicitly focused on analyzing the deposit morphology and its controllability.…”

A Comparison of Alternating Current and Direct Current Electrospray Ionization for Mass Spectrometry

“…Cone formation for AC ESI is significantly different from that for DC ESI, as confirmed by both experiment and theory [5,6], due to a mechanism termed “preferential entrainment.” This process can best be understood by considering the two half cycles separately during the AC ESI of an acidic protein solution. During the half cycle in which the spray emitter is at positive potential, more electrophoretically-mobile protons and less-mobile acidified proteins are attracted toward the tip of the spray cone.…”

“…After many cycles, repulsion forces between accumulated protein ions expel them in a narrow spray axial to the cone. The result is that the AC ESI cone is much narrower than the DC ESI cone with a half angle of approximately 12° for AC ESI [5,6] compared to 49° for DC ESI [7,8]. The preferential entrainment of analyte ions near the cone meniscus and narrower spray cone shape are thought to improve sensitivity during AC versus DC ESI.…”