Simulation and parametric study of a novel multi-spray emitter for ESI–MS applications

Abstract

In this work, we propose a novel carbon nanofiber (CNF) emitter for electrospray ionization (ESI)-mass spectrometry (MS) applications. The proposed emitter comprises an array of CNFs around the orifice of a microscale capillary. The electrospray ionization process is simulated using a CFD code based on Taylor-Melcher leaky-dielectric formulations for solving the electrohydrodynamics and volume-of-fluid (VOF) method for tracking the interface. The code is validated for a conventional multiple electrospray emitter and then applied to simulate the CNF emitter model. The modeling results show that under steady state condition, individual cone-jets are established around each of the CNFs resulting in an array of electrosprays. The approach being taken to fabricate the CNF emitter is briefly discussed. Effects of geometrical parameters including aspect ratio of CNFs, total number of CNFs and distribution pattern of the CNFs on the electrospray performance are studied. The influence of operating parameters such as flow rate, potential difference and physical properties of the solvent on the electrospray behavior is thoroughly investigated. The spray current, 'onset' potential and jet diameter are correlated with total number and distribution of CNFs and physical properties of the liquid. The correlation results are compared with the available results in the literature. Higher spray current and lower jet diameter indicate that the device can perform equivalent to nanospray emitters while using a micro-scale orifice. This allows higher sample throughput and eliminates potential clogging problem inherent in nano-capillaries.

Surface roughening of a non‐tapered open tubular emitter for improved electrospray ionization mass spectrometry performance at low flow rates

“…In order to attain stable electrospray signals at nano flow rates, tapered emitters were fabricated using techniques such as pulling or chemically etching fused silica to create 1 to 20 µm sized apertures 12–15. However, single‐tip tapered emitters with less than 20 µm diameter apertures often encounter problems such as clogging and larger flow resistance due to the nature of the smaller aperture 7, 16…”

“…These emitters proved robust to clogging and had improved nanoelectrospray performance compared to cleaved open tube and conventional emitters. Instead of forming a centered array of multiple electrospray emitters/channels, Knapp and co‐workers have proposed a multiple electrospray emitter comprising an array of carbon nanofibers (CNFs) around the orifice of a capillary 16. The proposed design would facilitate nanoelectrospray through a relatively large open tube.…”

Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures

“…In addition, the total ESI current generated at a given flow rate was shown to be proportional to the square root of the number of emitters allowing “brighter” ion sources [28]. The combined smaller charged droplets and high electric current has made the emitter array a promising ESI source for high sensitivity MS [25–34] and a variety of other applications such as nanoparticle synthesis [35], space propulsion [36], and microcombustion [37]. In the case of utilizing emitter array for MS analysis it is possible to tune the fabrication to further increase emitter density, but it is all of marginal benefit if the additional current generated cannot be efficiently delivered into the low pressure region of the mass spectrometer.…”

Nozzleless spray cooling using surface acoustic waves

“…Another technique known as electrohydrodynamic atomization or electrospraying (Cloupeau & Prunet-Foch, 1994;Nguyen et al, 2014;Wang & Mamishev, 2012a,b;Wilhelm et al, 2003) employs an electric field as the droplet generation mechanism wherein counterions in the fluid are attracted to the tip of the meniscus protruding from a nozzle when it is raised to an applied potential. Due to Coulombic repulsion, the tip, which deforms into a conical shape known as the Taylor cone (Taylor, 1964), subsequently disintegrates to produce a thin jet that breaks up due to Coulombic fission or hydrodynamic instabilities to form the droplets (Sen et al, 2007), which are then attracted to the surface of the collection electrode, which acts as the thermal exchange surface. While electrospray cooling is able to achieve high heat removal rates, a disadvantage of the technique is the requirement of a very high DC voltage supply ( $ 10 3 V).…”