Electrospray In Cone-jet Mode Research Articles

In searching of optimum electrospray ionization using both spray image and electric current measurement

Electrospray image and spray electric current measurement were used to experimentally characterize the optimum operating condition of the electrospray ionization process under different operating conditions, including electrospray flow rate (Q), solution electric conductivity (k) and the organic solvent content in the sample solution (Ro). It was first observed that a special cone-jet mode electrospray with extremely high stability could be obtained when the electrospray voltage was operated in a specific range (the optimum voltage range). In this mode, the spray current remains independent of spray voltage and the angle of electrospray (the optimum spray angle) was much larger than the ones in other modes of electrospray. The experimental results also showed that the optimum voltage range was dependent on multiple factors. The average value of the optimum voltage range (the optimum voltage) increased slightly as Q was increased and decreased significantly as Ro was increased. In addition, the optimum voltage would increase initially with the increase of k and become essentially independent of k at a sufficiently high solution electric conductivity. In contrast to a rather complicated parametric dependence of the optimum voltage range, the optimum spray angle was found to only depend on Q. It would increase initially as the increase of Q and remain to be constant when Q was higher than a specific value. The experimental results in this study allow one to maintain an optimum electrospray ionization under different operating conditions as required by the actual method of mass spectrometry analysis.

The influence of geometry on the flow rate sensitivity to applied voltage within cone-jet mode electrospray

This work investigates in greater detail than in previous studies the effect of geometry on the relationship between emitted flow rate and applied potential difference in cone-jet mode electrospray systems. The magnitude of the flow rate to voltage relationship is demonstrated to be sensitive to numerous geometric parameters. An explanation of this variation is offered; it is demonstrated that in the cone-jet mode of operation the change of flow rate with the applied extraction voltage is due to the change in electric field at the tip of the emitter. By a finite element method simulation of the assumed electrostatic process the analysis is further extended to include all geometric parameters. The results outlined show the change of flow rate with applied voltage in cone-jet mode electrospray can be significant. This dependence will, under some conditions, have a considerable effect on the electrospray flow rate, and consequently current and droplet size. This has implications on electrospray applications involving the use of the applied voltage to extract the sprayed solution, including nano-electrospray mass spectrometry techniques and some forms of electrospinning.

Formation of highly charged nanodroplets by condensation–electrospray device

A novel electrospray device is developed to generate highly charged nanodroplets from dew-condensed water. The device is composed of a discharge electrode with a spherical tip, ground electrode, Peltier cooling device, and high voltage power supply. When the surface temperature of the discharge electrode reaches the dew point of surrounding room air, a liquid water film is formed on the discharge electrode. Pulsating cone-jet mode electrospray is generated by applying negative 5kV high voltage to the discharge electrode. Highly charged macrodroplets are ejected from the tip of water cone and they are externally charged by the collision of unipolar negative ions. As the droplets shrink by the evaporation while keeping the number of charges, the droplets undergo Coulombic fission and/or electron emission when the number of charges exceeds the charge retention limits. The resulting change in the electrical mobility distribution and the number of charge are measured by the aerosol measurement techniques. It is found that droplets carry 3 to 23 elementary charges and the charge distribution has a peak at n=8.

Compact polymer multi-nozzles electrospray device with integrated microfluidic feeding system

Abstract Electrohydrodynamic (EHD) atomization consists in using an electric field for spraying a liquid flowing through a capillary. The applications are: mass spectrometry, colloid thrusters and more recently medicine nebulization processes. EHD atomization provides the ability to control the generated droplets size by adjusting electrospray parameters. It is however essential to manufacture the emitters into arrays because flow through a stable cone-jet mode electrospray can only be maintained at low flow rate and most applications require a high throughput. We propose a new design of a multiple electrospray system involving an innovative nozzle shape and flow restrictor system. Nozzles and microfluidic restrictor system are manufactured on the same polycarbonate sheet using the excimer laser technology and thus allowing a high compactness of this system.

Effect of emitter geometry on flow rate sensitivity to voltage in cone jet mode electrospray

The effect of voltage on flow rate within cone jet mode electrospraying has been investigated, with particular emphasis on the effect of emitter geometry. A set of experiments investigated the effect of the outer and inner diameters on the flow rate relationship to voltage, in cone jet mode electrospray. This was accomplished by the use of a high fidelity flow meter, capable of measuring changes in flow rate to a fraction of a nanolitre per second.It has been previously demonstrated that there are two separate parameters that influence the flow rate sensitivity to voltage; the hydraulic resistance of the flow system, and the outer diameter of the emitter. By a simple derivation, the second of these two is explained by the variation of theoretical electric pressure with voltage, as the outer diameter is varied.Good agreement is found between experimental and theoretical results, suggesting the simple theory reasonably explains the physics of the situation.As well as elucidating the physics involved in electrospray—suggesting the electric field is an important controlling parameter within cone jet mode electrospray—the theoretical and experimental agreement has important implications for variable throttling of thrust in colloid thrusters, and could bring about better optimization of performance in other electrospray-employing fields.

Elastomeric microchip electrospray emitter for stable cone-jet mode operation in the nanoflow regime.

Despite widespread interest in combining laboratory-on-a-chip technologies with mass spectrometry (MS)-based analyses, the coupling of microfluidics to electrospray ionization (ESI)-MS remains challenging. We report a robust, integrated poly(dimethylsiloxane) microchip interface for ESI-MS using simple and widely accessible microfabrication procedures. The interface uses an auxiliary channel to provide electrical contact for the stable cone-jet electrospray without sample loss or dilution. The electric field at the channel terminus is enhanced by two vertical cuts that cause the interface to taper to a line rather than to a point, and the formation of a small Taylor cone at the channel exit ensures subnanoliter postcolumn dead volumes. Cone-jet mode electrospray was demonstrated for up to 90% aqueous solutions and for extended durations. Comparable ESI-MS sensitivities were achieved using both microchip and conventional fused silica capillary emitters, but stable cone-jet mode electrosprays could be established over a far broader range of flow rates (from 50-1000 nL/min) and applied potentials using the microchip emitters. This attribute of the microchip emitter should simplify electrospray optimization and make the stable electrospray more resistant to external perturbations.

The sensitivity of volumetric flow rate to applied voltage in cone-jet mode electrospray and the influence of solution properties and emitter geometry

A high accuracy online flow rate measurement system has been used to demonstrate the effect of applied voltage, Vapp, on the volumetric flow rate, Q, through an electrospray system. Several solutions of the organic solvents ethylene and triethylene glycols doped with sodium iodide to give varying conductivities in the range of 0.0025–0.23S∕m have been sprayed. It was established for the first time that solution conductivity has no appreciable effect on the sensitivity of flow rate to applied voltage in the cone-jet mode of electrospray. However, it appears that even when the hydraulic resistance is taken into account, the sensitivity of flow rate as controlled by the applied voltage is additionally related to the emitter exit geometry. These findings are of particular importance to both spacecraft propulsion and electrospray mass spectrometry technologies and suggest careful emitter geometry design considerations will lead to greater control over electrospray properties.

Formation of ceramic thin films using electrospray in cone-jet mode

An electrostatic atomization technique has been developed to generate ultrafine spray droplets of ZrO/sub 2/ and SiC ceramic suspensions in a range of a few micrometers with a narrow size distribution. The aim of this paper is to deposit uniform thin films (from a few micrometers to a few tens of micrometers) of these ceramic materials on alloy substrates. Compared to some other thin-film deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), and plasma spray (PS), etc., the thin-film deposition process using electrostatic atomization is not only cheap but also capable of depositing a very thin multilayer with abrupt interfaces. CVD and PVD are expensive techniques. They require either a high vacuum, even an ultrahigh vacuum environment or complex gas handling system. Their deposition rate is also low. PS is normally used to grow thermal barrier coatings which usually have a thickness of a few tens to a few hundreds micrometers. Its application is limited by the quality of the coatings (high porosity, coarse and nonuniform microstructure). Preliminary results in this work have shown that, for low through-put atomization, the cone-jet is the most suitable method to produce a fine charged aerosol with a narrow size distribution, which is crucial to produce uniform thin films. It was found that the size of ceramic particles in ZrO/sub 2/ and SiC thin films is less than 10 /spl mu/m. Microstructures of these thin films show very homogenous morphologies. These results indicate that ceramic thin films with high homogeneity can be deposited using electrostatic atomization. It was also observed that the morphology of the underlayer has some influence on the morphology of the top layer.

Formation of ceramic thin films using electrospray in cone-jet mode

The electrospray technique has been developed to generate fine droplets of SiC and ZrO/sub 2/ ceramic suspensions and to deposit these ceramic thin films and their bilayer on alloy substrates. SEM examinations of the microstructures of these thin films show that the films are very homogenous with a uniform particle size less than 10 /spl mu/m. The deposition of a very thin bilayer with an abrupt interface indicates that the electrospray process can be well controlled. The theoretical prediction of droplet size and electric current is in good agreement with experimental results, indicating that fine suspension droplets can be generated in the cone-jet mode. Therefore it can be concluded that electrospray is a promising technique for the preparation and controllable distribution of uniform ceramic thin films and coatings with the added advantage of low cost. It could find a wide range of industrial applications in the future.