Electrosprays electrostatic sprays

Electrospray (ES) existed long before its application to mass spectrometry (MS). It is a method of considerable importance for the electrostatic dispersion of liquids and creation of aerosols. The interesting history and notable research advances in that field are very well described in Bailey s book Electrostatic Spraying of Liquids. 37 Much of the theory concerning the mechanism of the charged droplet formation was developed by researchers in this area. The latest works can be found in a special issue38 of the Journal of Aerosol Science devoted to ES. 

Electrospray, also called electrohydrodynamic or electrostatic spray, is an atomization technique in which liquids are dispersed solely by the application of high voltages. A simple electrospray setup is shown in Fig. 4. A liquid flows into a metal capillary tube charged to the kilovolt range and emerges from the tip as a conical meniscus, known as a Taylor cone, due to the intense electric field (Fig. 5). An unstable jet extends continuously from the apex of the cone and disperses into charged droplets further downstream. Electrosprays have been used in industrial... 

Gomez, A. The electrospray and its application to targeted drug inhalation. Respir. Care 2002, 47 (12), 1419-1433. Cloupeau, M. Prunet-Foch, B. Electrostatic spraying of liquids in cone-jet mode. J. Electrostal. 1989, 22, 135-159. 

Ramsey and Ramseyalso described microchip interfacing to an ion trap mass spectrometer. Microfluidic delivery was realized by electroosmotically induced pressures and electrostatic spray at the channel terminus was achieved by applying a potential between the microchip and a conductor spaced 3-5 mm from the channel terminus. Tetrabutylammonium iodide was tested as a model compound with this device. Later, Ramsey et reported use of a microchip nanoelectrospray tip coupled to a time-of-flight mass spectrometer for subattomole sensitivity detection of peptides and proteins. A fluid delivery rate of 20-30 nL/min was readily obtained by applying an electrospray voltage to the microchip and the nanospray capillary attached at the end of the microfabricated channel without any pressure assistance. 

Electrospray (Fig. 8.4) is a process where a high potential is applied onto a liquid to generate a fine aerosol. Electrospray or electrostatic spraying has been applied to electrostatic painting, rocket propulsion, or fuel atomization. The phenomenon of electrospray was observed and investigated long before it was practical to the analysis of gas-phase ions transferred from solution into a mass spectrometer. One of the earliest reports of the effect of an electrical tension applied to a liquid was made in 1600 by William Gilbert. He observed that a... 

The first reported electrostatic spraying of a liquid was described by Jean-Antoine NoUet in 1750, long before the term electrospraying was even coined. 

Electroslag remelting, 23 255 Electroslurry process, 23 576 Electrospinning, 11 186 Electrospray ionization, liquid chromatography, 4 625 Electrospray ionization source, 15 654-658 Electrostatic atomization, in spray coating, 7 72-73... 

Electrospray ionization (ESI) refers to the overall process by which an intense electric field disperses a sample liquid into a bath gas as a fine spray of highly charged droplets. Evaporation of those charged droplets produces gas-phase ions by mechanisms that remain the subject of much argument and debate. The ESI is a complex of independent component processes, the two most important of which are electrospray dispersion, the electrostatic dispersion of sample liquid into charged droplets, and ionization, the transformation of solute species in those droplets to free ions in the gas phase. 

The nano-electrospray (nanoES) source is essentially a miniaturized version of the ES source. This technique allows very small amounts of sample to be ionized efficiently at nanoliters per minute flow rates and it involves loading sample volumes of 1-2 pi into a gold-coated capillary needle, which is introduced to the ion source. Alternatively for on-line nanoLC-MS experiments the end of the nanoLC column serves as the nanospray needle. The nanoES source disperses the liquid analyte entirely by electrostatic means [27] and does not require assistance such as solvent pumps or nebulizing gas. This improves sample desolvation and ionization and sample loading can be made to last 30 minutes or more. Also, the creation of nanodroplets means a high surface area to volume ratio allowing the efficient use of the sample without losses. Additionally, the introduction of the Z-spray ion source on some instruments has enabled an increase in sensitivity. In a Z-spray ion source, the analyte ions follow a Z-shaped trajectory between the inlet tube to the final skimmer which differs from the linear trajectory of a conventional inlet. This allows ions to be diverted from neutral molecules such as solvents and buffers, resulting in enhanced sensitivity. 

Figure 9.7 Schematic of Electrospray ionization. A "spray" of droplets is formed that evaporate until the destabilizing electrostatic forces cause the droplets to "explode" releasing multi-charged molecular ion species for mass analysis.

Electrospray ionisation generates analyte ions this is accomplished by spraying the eluent (mobile phase solvent + any analytes eluting from the EC system) into a chamber at atmospheric pressure. This is done in the source in the presence of a heated drying gas (usually Nj) and a strong electrostatic field. The pressure of the electrostatic field causes further dissociation of the analyte molecules and the drying gas causes the solvent to evaporate (see Figure 5.16). 

Abstract This chapter provides an introduction to electrosprays (ES). Electrosprays, also known as Electrohydrodynamic (EHD) sprays, are sprays created from the atomization of a bulk liquid due to electrostatic charging. The fundamental physics involved in such sprays is first introduced followed by results of experimental and theoretical characterization. Practical applications are briefly discussed with special attention paid to the use of electrospray in mass spectrometry where it is used as an ion source. 

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