Electrospray Characteristic Curves:  In Pursuit of Improved Performance in the Nanoflow Regime

Marginean, Ioan; Page, Jason S.; Smith, Richard D.

doi:10.1021/ac0707986

Cited by 55 publications

(70 citation statements)

References 49 publications

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“…For optimal sample utilization, determination of the parameters that provide the highest signal intensity is crucial. Many previous studies have been performed to optimize different parameters that affect the ESI signal, like sheath flow [10,12,20], nebulizing gas [13,16], buffer systems [20,30], and ESI voltage [31,32]. Likewise, ESI emitters have been extensively studied because the characteristics of the emitter, such as the emitter i.d., the surface area of the emitter orifice, and the hydrophobicity, have a great impact on the observed ESI signal; in addition to influencing the working parameters of the system, such as flow rate or ESI voltage [33].…”

Section: Introductionmentioning

confidence: 99%

A Study of Electrospray Ionization Emitters with Differing Geometries with Respect to Flow Rate and Electrospray Voltage

Reschke

Timperman

2011

J. Am. Soc. Mass Spectrom.

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The performance of several electrospray ionization emitters with different orifice inside diameters (i.d.s), geometries, and materials are compared. The sample solution is delivered by pressure driven flow, and the electrospray ionization voltage and flow rate are varied systematically for each emitter investigated, while the signal intensity of a standard is measured. The emitters investigated include a series of emitters with a tapered outside diameters (o.d.) and unaltered i.d.s, a series of emitters with tapered o.d.s and i.d.s, an emitter with a monolithic frit and a tapered o.d., and an emitter fabricated from polypropylene. The results show that for the externally etched emitters, signal was nearly independent of i.d. and better ion utilization was achieved at lower flow rates. Furthermore, emitters with a 50 μm i.d. and an etched o.d. produced about 1.5 times more signal than etched emitters with smaller i.d.s and about 3.5 times more signal than emitters with tapered inner and outer dimensions. Additionally, the work presented here has important implications for applications in which maximizing signal intensity and reducing frictional resistance to flow are necessary. Overall, the work provides an initial assessment of the critical parameters that contribute to maximizing the signal for electrospray ionization sources interfaced with pressure driven flows.

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Section: Introductionmentioning

confidence: 99%

A Study of Electrospray Ionization Emitters with Differing Geometries with Respect to Flow Rate and Electrospray Voltage

Reschke

Timperman

2011

J. Am. Soc. Mass Spectrom.

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“…Increased evaporation rate leads to lower effective electrospray flow rates, which generate smaller currents at the same voltage. 29 To provide the same current at lower pressures, the voltage should increase-a trend opposing that observed experimentally. Based on the I ϳ Q 1/2 scaling law, 33 the current should decrease by less than 1% for a 2% evaporation rate; to offset this current drop the voltage applied to an electrospray generating 100 nA at 200 nL/min needs to increase by 4-5 V, depending on the chamber pressure.…”

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confidence: 90%

“…To ensure improved reproducibility and greater confidence in the experimental data, the present studies were performed at flow rates between 100 and 300 nL/ min. Because the flow rates are outside the cone-jet stability island, 29 the electrospray was operated in the pulsating regime; under these conditions, the electrospray current increased linearly with the applied voltage.…”

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confidence: 99%

Effect of pressure on electrospray characteristics

Marginean

Page

Smith

2009

Applied Physics Letters

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An experimental study of pulsating electrosprays operated at subambient pressure is reported. The pressure domain that affords stable electrospray operation appears to be limited by the vapor pressure of the liquid. The voltage driving the electrospray is shown to have a logarithmic dependence on pressure. The observed scaling amends the relationship currently used to calculate the electric field at the tip of the meniscus of an electrified liquid. © 2009 American Institute of Physics. ͓doi:10.1063/1.3258494͔ Zeleny 1 conducted the first rigorous studies of what he described as discharges from liquid points, phenomena known today as electrosprays. In his experiments, a minimal pressure difference delivered electrified liquid at the tip of a glass capillary for spraying against a planar counterelectrode. In a similar geometry, Eyring et al.2 studied the electric field E when applying a voltage V between a hyperbolic metal electrode polished to a radius of curvature r and a metallic disk situated at a distance d. In a simplified form, the electric field was expressed as a function of a constant c:This relationship is currently in use to estimate the electric field at the tip of a rounded liquid meniscus. A semispherical liquid drop is in equilibrium if the pressure drop across the liquid interface ͑p − p 0 ͒ is balanced by its surface tension ͑␥͒ : p − p 0 = ␥ / r, where r is the radius of curvature of the meniscus. Under the influence of E, r changes to compensate for the pressure produced by electrical forces p E = 0 E 2 / 2, where 0 is vacuum permittivity. Once the electric field surpasses a threshold at a critical voltage, a singularity is induced, which reshapes the meniscus into a cone and triggers the ejection of charged liquid from its apex. [4][5][6] The cone-jet electrospray regime 7 is established if the charge is generated electrochemically at the same rate as it is ejected; however, when operated close to the threshold electric field, supply disruptions lead to discontinuous regimes that have been described as burst, 8 pulsating, 9 or astable. 10One of the most important applications of electrosprays is in mass spectrometry ͑MS͒ ionization sources. 11 The small charged droplets experience cycles of solvent evaporation followed by charge reduction through Rayleigh fission events or field evaporation.12-15 The charged aerosol produced by electrosprays at atmospheric pressure must be transferred into a very low pressure environment for the MS analyses. This is generally accomplished by several stages of differential pumping. Ion funnels 16 can be employed to improve the ion transfer efficiency through intermediate chambers in the 1-30 torr range, while traditional radio frequency ͑rf͒ ion guides are broadly used in lower pressure regimes. A typical electrospray ionization ͑ESI͒-MS interface employs a heated capillary inlet enabling sampling of the electrospray while providing supplemental thermal energy to aid desolvation of the charged droplets. Most of the charged aerosol is "lost" to the front or insi...

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“…38 Additionally, we can find scaling laws to relate the input parameters of the system, basically the flow rate Q and the applied voltage drop V, with the output parameters, i.e., the electrical current transported by the liquid I and the droplets size d. Along the paper, we will use the scaling laws developed by Loscertales and de la Mora 16 and by Gañan et al 39 They are mostly applicable when high conductivity liquids with intermediate viscosities are operated at small flow rates in a gaseous medium. In the following, we show the scaling laws for the electrical current and for the droplet size, expressed in dimensionless form…”

Section: Scaling Laws In Electrospraysmentioning

confidence: 99%

Surface tension effects on submerged electrosprays

2012

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Electrosprays are a powerful technique to generate charged micro/nanodroplets. In the last century, the technique has been extensively studied, developed, and recognized with a shared Nobel price in Chemistry in 2002 for its wide spread application in mass spectrometry. However, nowadays techniques based on microfluidic devices are competing to be the next generation in atomization techniques. Therefore, an interesting development would be to integrate the electrospray technique into a microfluidic liquid-liquid device. Several works in the literature have attempted to build a microfluidic electrospray with disputable results. The main problem for its integration is the lack of knowledge of the working parameters of the liquid-liquid electrospray. The "submerged electrosprays" share similar properties as their counterparts in air. However, in the microfluidic generation of micro/nanodroplets, the liquid-liquid interfaces are normally stabilized with surface active agents, which might have critical effects on the electrospray behavior. In this work, we review the main properties of the submerged electrosprays in liquid baths with no surfactant, and we methodically study the behavior of the system for increasing surfactant concentrations. The different regimes found are then analyzed and compared with both classical and more recent experimental, theoretical and numerical studies. A very rich phenomenology is found when the surface tension is allowed to vary in the system. More concretely, the lower states of electrification achieved with the reduced surface tension regimes might be of interest in biological or biomedical applications in which excessive electrification can be hazardous for the encapsulated entities.

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Electrospray Characteristic Curves: In Pursuit of Improved Performance in the Nanoflow Regime

Cited by 55 publications

References 49 publications

A Study of Electrospray Ionization Emitters with Differing Geometries with Respect to Flow Rate and Electrospray Voltage

A Study of Electrospray Ionization Emitters with Differing Geometries with Respect to Flow Rate and Electrospray Voltage

Effect of pressure on electrospray characteristics

Surface tension effects on submerged electrosprays

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