Droplet Dynamics Changes in Electrostatic Sprays of Methanol−Water Mixtures

Olumee, Zohra; Callahan, John H.; Vertes, Akos

doi:10.1021/jp982027z

Cited by 82 publications

(99 citation statements)

References 27 publications

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“…With a gas pressure of 45 bar, the velocity was 600 m/s at the outlet of the outer capillary and decreased to 16 m/s 10 mm from the emitter. The average droplet velocity is around 10 m/s in the stable electrospray plume without the nebulizer gas [18,19].…”

Section: Nebulizer Gas Flow Effect On the Electrosprayed Droplets Nummentioning

confidence: 99%

The Role of Nebulizer Gas Flow in Electrosonic Spray Ionization (ESSI)

Wang

Allmendinger

Zhu

et al. 2011

J. Am. Soc. Mass Spectrom.

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In this work, we investigated the role of the nebulizer gas flow in electrosonic spray ionization (ESSI), by systematically studying the relation between the flow and the ion signals of proteins, such as cytochrome c and holomyoglobin using ESSI-mass spectrometry (MS). When a neutral solution was delivered with a small sample flow rate (≤5 μL/min), no obvious transition from electrospray ionization (ESI) to ESSI was found as the gas velocity varies from subsonic to supersonic speed. Droplets mostly experienced acceleration instead of breakup by the high-speed nebulizer gas. On the contrary, using particular experimental conditions, such as an acidic solution or high sample flow rate (≥200 μL/min), more folded protein ions appear to be kept in droplets of diminishing size due to breakup by the high-speed nebulizer gas in ESSI compared with ESI. Theoretical analyses and numerical simulations were also performed to explain the observed phenomena. These systematic studies clarify the ionization mechanism of ESSI and provide valuable insight for optimizing ESSI and other popular pneumatically assisted electrospray ionization methods for future applications.

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Section: Nebulizer Gas Flow Effect On the Electrosprayed Droplets Nummentioning

confidence: 99%

The Role of Nebulizer Gas Flow in Electrosonic Spray Ionization (ESSI)

Wang

Allmendinger

Zhu

et al. 2011

J. Am. Soc. Mass Spectrom.

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“…As a complement to MS, we thus used phase Doppler anemometry (PDA) in this work. PDA is a powerful tool to directly measure the droplet size, velocity, and number density in dynamic processes such as electrospray [19][20][21] or desorption electrospray ionization [22]. The size, velocity, and density of droplets in the intersection where two sprays meet (referred to as the origin in the following) and 2 mm downstream from the cross-section were measured.…”

Section: Introductionmentioning

confidence: 99%

On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration

et al. 2011

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Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet-droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet-droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet-droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the sheath gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet-droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be <5 μs. This work gives a clear picture of droplet-droplet interactions in the dual-spray EESI process and detailed information for the optimization of this method for future applications that require higher sensitivity.

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“…In this study, we combined spatially resolved fluorescence measurements with phase Doppler anemometry, which allows the measurement of droplet sizes, numbers, and velocities [22,23].°The°evolution°of°an°equilibrium°in the spray plume with decreasing droplet size was probed. As a first model system we used rhodamine B-sulfonylchloride (RBS), which forms dimers at higher concentrations.…”

mentioning

confidence: 99%

Shrinking droplets in electrospray ionization and their influence on chemical equilibria

Wortmann

Kistler-Momotova

Zenobi

et al. 2007

J. Am. Soc. Mass Spectrom.

117

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We investigated how chemical equilibria are affected by the electrospray process, using simultaneous in situ measurements by laser-induced fluorescence (LIF) and phase Doppler anemometry (PDA). The motivation for this study was the increasing number of publications in which electrospray ionization mass spectrometry is used for binding constant determination. The PDA was used to monitor droplet size and velocity, whereas LIF was used to monitor fluorescent analytes within the electrospray droplets. Using acetonitrile as solvent, we found an average initial droplet diameter of 10 m in the electrospray. The PDA allowed us to follow the evolution of these droplets down to a size of 1 m. Rhodamine B-sulfonylchloride was used as a fluorescent analyte within the electrospray. By spatially resolved LIF it was possible to probe the dimerization equilibrium of this dye. Measurements at different spray positions showed no influence of the decreasing droplet size on the monomer-dimer equilibrium. However, with the fluorescent dye pair DCM and oxazine 1 it was shown that a concentration increase does occur within electrosprayed droplets, using fluorescence resonance energy transfer as a probe for the average pair distance. ( An important aspect of the highly dynamic electrospray process concerns the shrinking droplets. After the droplet creation, solvent evaporation and Coulomb explosions lead to a decrease of droplet size until all solvent has evaporated and the final desolvated and ionized analytes are produced. A decrease of droplet size resulting from solvent evaporation will lead to a concentration increase of nonvolatile analytes within the droplets. For dissolved species that participate in a chemical equilibrium, such as free and bound states of partners that can form a noncovalent complex, the question arises whether the increasing concentrations affect the equilibrium position. Given that binding constant determination with ESI-MS usually relies on measuring the relative amounts of free and bound species, a perturbation of the equilibrium introduced by the shrinking droplets would influence the results of such an experiment. Recent studies show that the time between droplet creation and production of desolvated ions in ESI is within milliseconds [5]. In other words, if the association and dissociation reactions are fast, an equilibrium should be able to track a concentration increase within the droplets.The shrinking droplet volume also leads to Coulomb explosions/droplet fission, when the mutual repulsion of charges is high enough to overcome the surface tension of the droplet. The parent droplet ejects several smaller offspring droplets, which together carry 10 -25% of the charge, but only about 5% of the mass of the original droplet [9]. These offspring droplets then segregate within the electrospray, as shown theoretically by Wilhelm et al. [10]. Analytes will not generally be evenly distributed between the parent and offspring droplets. Partitioning processes, which have been investigated by several research g...

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Droplet Dynamics Changes in Electrostatic Sprays of Methanol−Water Mixtures

Cited by 82 publications

References 27 publications

The Role of Nebulizer Gas Flow in Electrosonic Spray Ionization (ESSI)

The Role of Nebulizer Gas Flow in Electrosonic Spray Ionization (ESSI)

On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration

Shrinking droplets in electrospray ionization and their influence on chemical equilibria

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