Charge reduction electrospray mass spectrometry

A new mass spectrometric technique, charge reduction electrospray mass spectrometry (CREMS), allowing the analysis of complex mixtures of biological molecules is described. The charge state of ions produced by electrospray ionization may be reduced in a controlled manner to yield predominantly singly charged ions through reactions with bipolar (i.e., both positively and negatively charged) ions generated using a 210Po alpha particle source. The electrospray-generated multiply charged ions undergo charge reduction in a "neutralization chamber" positioned before the entrance nozzle to the mass spectrometer. The ions are detected using a commercial orthogonal electrospray time-of-flight mass spectrometer, although the neutralization chamber can be adapted to virtually any mass analyzer. The CREMS results obtained exhibit a signal intensity drop-off with increasing oligonucleotide size similar to that observed with matrix-assisted laser desorption/ionization mass spectrometry. Proton-transfer reactions were found to be responsible for reducing charge on proteins and oligonucleotides in both positive and negative ion mode.     

Corona discharge in charge reduction electrospray mass spectrometry

Corona discharge is applied to charge reduction electrospray mass spectrometry for the analysis of complex mixtures of biological molecules. Recent work has described a method of charge reduction (reducing the charge states of analyte ions generated by the electrospray process) employing the radioactive isotope 210Po to produce neutralizing species. A variation to this approach is presented, in which charge neutralization is mediated by ions produced in a corona discharge. Varying the corona discharge voltage controls the current and the degree of charge reduction, providing predominantly singly charged ions that are detected by a commercial electrospray time-of-flight mass spectrometer. This technique provides charge reduction for the simplification of ESI spectra, without need for any radioactive material.     

Effects of Powder Velocity and Contact Materials on Tribocharging of Polymer Powders for Powder Coating Applications

Electrostatic powder deposition using corona charging is widely used in a plethora of industrial applications. Disadvantages of this technique are back corona onset and the Faraday penetration limitation. Another method to charge powders is to use tribochargers. Tribocharging depends upon the work function difference between the contacting materials and generates bipolarly charged particles. In this study, acrylic and epoxy powders were fluidized and charged by passing through stainless steel, copper, aluminum, and polycarbonate static mixers, respectively. The particle velocity and powder flow rate were varied to determine their effect on the net charge-to-mass ratio (Q/M) acquired by the powders. The Q/M increased rapidly with velocities between 1.5 to 2.5 m/s and stabilized for higher velocities but decreased with increasing powder flow rate at a constant velocity. The net positive or negative charge on each powder was determined to be dependant on the charger material. The use of an aluminum charger (net negative charge) in combination with a PTFE finger nozzle (net positive charge) resulted in a net powder Q/M of - 0.05 μC/g. The generation of an ion-free powder cloud with high bipolar charge but overall charge density of almost zero is anticipated to provide a better coverage of recessed areas.     

Dual needle corona discharge to generate stable bipolar ion for neutralizing electrosprayed nanoparticles

The performances of dual needle corona discharge (NCD) as bipolar ion source to neutralize the electrospray (ES) particles were characterized and optimized. The NCD was constructed from a tungsten needle and grounded mesh electrode in the needle-to-plane configuration. The dual NCD created a bipolar ion environment by mixing the balanced concentration of positive and negative ions produced by each NCD. The dual NCD was placed in an electrospray aerosol generator (EAG) apparatus to reduce the charge state of the ES particles. Polystyrene latex (PSL) suspensions having the particle size range of 96–256 nm were used as the precursor solution for the electrospray process. Some characterizations to the NCD were carried out to obtain optimum operating voltage and air flow rate. The size distribution and charge fraction of the electrospray PSL (ES-PSL) particles exiting the EAG were also investigated. The result showed the dual NCD could generate stable bipolar ions by mixing positive and negative ions with balanced concentration. The bipolar ions from the dual NCD were capable of neutralizing and reducing the charge state of highly charged ES-PSL particles larger than 100 nm. The EAG, equipped with the dual NCD, could generate ES-PSL particles with stable concentration and consistent size distribution. The charge fraction calculation of the ES-PSL particles showed that more than 80% of the particles exiting the EAG were positively charged.     

Electrostatic Evaluation of a Unipolar Diffusion and Field Charger of Aerosol Particles by a Corona Discharge

This article presents a unipolar diffusion and field charger by corona discharge is presented and electrostatically evaluated for charging aerosol particles. The electrostatic characteristics of the charger were investigated with an electrometer by measuring the ion number concentrations corresponding to the discharge and charging currents. The discharge and charging currents, and ion number concentration in the discharge and charging zones of the charger, increased with corona voltage. The magnitudes of the ion number concentration for positive and negative coronas in the discharge zone ranged from 1.34 × 10¹³ to 1.84 × 10¹⁵ ions/m³ and 7.34 × 10¹³ to 2.64 × 10¹⁵ ions/m³, respectively. For the charging zone, the ion number concentrations for positive and negative coronas ranged from 2.95 × 10¹³ to 1.52 × 10¹⁴ ions/m³ and 2.06 × 10¹³ to 1.47 × 10¹⁴ ions/m³, respectively. To predict the behavior of the electric field strength and lines in the discharge and charging zones of the charger, the electric field strength and distribution of the charger in the discharge and charging zones were calculated by a commercial computational fluid dynamics software package. Numerical calculation results of electric field distribution and lines through the inner electrode showed good agreement with experimental results. Also, the mean charge per particle for particle diameters were in the range of 0.01 to 50 µm for various operating conditions of the charger was theoretically evaluated. For both diffusion and field charging, lower aerosol flow rate and higher corona voltage resulted in an increase in the mean charge per particle within the charger. This simple charger proved to be particularly useful in diffusion and field charging of aerosol particles in particulate matter detector instruments for measuring PM10 and PM2.5 concentration.     

Effect of X-ray energy and ionization time on the charging performance and nanoparticle formation of a soft X-ray photoionization charger

The present study is a detailed analysis of the charging performance of aerosol nanoparticles using soft X-ray photoionization. The study includes methods used to suppress the formation of unnecessary nanoparticles during ionization. Using a soft X-ray ionizer, the charging performance was evaluated at different emitting energies (3, 4 and 9.5 keV) and for ionization time and chamber type. The results were compared with the charging performance of an Am-241 α-ray ionizer. The experimental results showed that the total charging ratio for monodispersed nanoparticles is similar between X-ray and α-ray ionizers. However, a considerable amount of nanometer-sized particle formation caused by X-ray photoionization also was detected. Particle generation was significantly dependent on gas residence time in the ionization chamber, which was caused by ion-induced nucleation. Overall, the soft X-ray photoionizer is a more suitable bipolar diffusion charger because of a superior capacity for charging large numbers of dense aerosol particles in a relatively short residence time, which can be controlled in the ionization chamber.     

Development of a Compact Electrostatic Nanoparticle Sampler for Offline Aerosol Characterization

A compact electrostatic nanoparticle sampler has been developed to support the offline analysis of nanoparticles via electron microscopy. The basic operational principle of the sampler is to electrically charge particles by mixing nanoparticles and unipolar ions produced by DC corona discharge, and electrostatically collecting charged particles. A parametric study was first performed to identify the optimal operating condition of the sampler: a total flow rate (i.e., the sum of the particle and ion carrier flow rates) of 1.0 lpm, an aerosol/ion carrier flow rate ratio of 1.0, and a collection voltage of 4.5 kV. Under the above condition, the sampler achieved a collection efficiency of more than 90 % for particles ranging from 50 to 500 nm. The effect of particle material on the sampler’s performance was also studied. The prototype had lower collection efficiencies for oleic acid particles than for sodium chloride particles in the size range from 50 to 150 nm, while achieving a comparable efficiency in the size range large than 150 nm. Effects of particle diameter, particle material, and total flow rate on the sampler’s collection efficiency are explained by the particle charging data, i.e., charging efficiencies and average charges per particle.     

Fringing field directed assembly of nanomaterials

This letter reports on a new gas-phase printing approach to deposit nanomaterials into addressable areas on a surface with 50 nm lateral accuracy. Localized fringing fields that form around conventional resist patterns (PMMA and SiO2) with openings to a silicon substrate are used to direct the assembly of nanomaterials into the openings. Directed assembly was observed due to a naturally occurring inbuilt charge differential at the material interface that was further enhanced by corona charging to yield a field strength exceeding 1 MV/m in Kelvin probe force microscopy (KFM) measurements. The assembly process is independent of the nanomaterial source and type: an evaporative, plasma, and electrospray source have been tested to deposit silicon and metallic nanoparticles. The results suggest a potential route to form nanolenses on the basis of charged resist structures; a 3-fold size reduction has been observed between the structures and the assembled particles. Applications range from the integration of functional nanomaterial building blocks to the elimination of lift-off steps in semiconductor processing.     

Corona discharge neutralizer for electrospray aerosols used with condensation nucleation light-scattering detection

To obviate the use of radioactive materials, a simple unipolar electrical neutralizer based on a corona discharge was developed to neutralize electrospray aerosols used when coupling capillary liquid chromatography (CLC) and capillary electrophoresis (CE) to condensation nucleation light-scattering detection (CNLSD). The electrical neutralizer could be operated with either a positive or negative corona to generate ions to neutralize oppositely charged aerosols generated by electrospray and allow sensitive detection with CNLSD. The device could further be operated with organic solvents as well as aqueous buffer. The parameters affecting the corona discharge and neutralization process were studied and optimized. Compared to a CNLSD system using a radioactive neutralizer, the system with the electrical neutralizer showed higher signal and signal-to-noise ratio for test compounds, which indicated better neutralization efficiency of the charged aerosol. Highly reproducible results were obtained with the robust and durable electrical neutralizer with both CLC- and CE-electrospray-CNLSD systems.     

Enhancing fine particle separation by hybrid-electrostatic-turbulence coagulation: An experimental and numerical investigation

The electrostatic precipitator(ESP) has low efficiency in removing sub-micron particles. Coagulation technology, as a fine particle pretreatment technology, uses an external effect to agglomerate and grow fine particles, increase the average particle size, and make it easier to remove by subsequent dust removal equipment. However, the coagulation efficiency of a single coagulation technology is limited. Aiming at the particle charging mechanism and coagulation mechanism in the electric/turbulent composite coagulation process of fine particles, this paper uses a combination of numerical simulation and experiment to study the effects of different structural parameters, discharge parameters and flue gas parameters on corona discharge and particle charge. On this basis, the coagulation characteristics of charged particles in the turbulent flow field are studied. The results show that, when the Angle between the tip of the arista electrode is 90°, the corona discharge effect is the best. With the increase of supply voltage and temperature, the charge of particles increases. When the applied positive voltage is 29 kV and negative voltage is ?35 kV, the total coagulation coalescence efficiency of fine particles reaches the maximum. The coagulation efficiency increases with the increase of temperature, but decreases with the increase of inlet flow rate.     

COLLECTION MECHANISMS OF ELECTRET FILTER

Collection efficiency of a single electret fiber, which carries permanent positive and negative charges, was studied. Theoretically, it was obtained by solving the equation of particle motion taking account of the induced and Coulombic forces simultaneously. When either induced or Coulombic forces dominates particle collection, the collection efficiency was found to be proportional to 2/5 power of induced force parameter K_In, and 3/4 power of Coulombic force parameter K_C, respectively. However, when both forces are effective simultaneously, the efficiency was not expressed by the simple superposition of both effects because of negative interaction between both forces. Experimentally, collection efficiency of a single electret fiber was measured by using monodisperse sodium chloride particles ranging from 0.01 to 0.4 μm in diameter for filtration velocities from 5 to 200 cm/s, under different charging state of particles, i.e., uncharged, singly or doubly charged and charged in Boltzmann equilibrium.

It was found that the experimental efficiency was markedly influenced by the small change in the charging state of particles, and that both Coulombic and induced forces affect the collection of charged particles simultaneously. The dependency of experimental collection efficiency on dimensionless parameters K_In and K_C coincided with the theoretical calculation. Based on the theoretical and experimental results, the following semi-empirical expression for the single fiber collection efficiency, which is applicable to particles in any charging state, was presented.

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25kV/2A谐振式恒流充电电源

为 1MJ 电容器储能系统研制了一台输出电压 25kV,输出电流2A的恒流充电电源。该电源采用零电流切换非连续全波谐振原理。串联 LC 谐振电路由接成全桥形式的4只大功率 IGBT 驱动,谐振频率固定为 80kHz,开关工作频率 30-65kHz 可调。谐振产生的非连续正弦形电流经匝比为 1:50 的高压变压器升压至 25kV,经快恢复高压二极管串组成的全桥电路整形为一系列非连续的半正弦状电流脉冲,给 10000μF 高压电容器组充电。最终充电电压和充电电流的大小由微处理器控制,前者正比于充电电流脉冲的总个数,后者则正比于开关工作频率。     

Development and testing of a detection method for liquid chromatography based on aerosol charging

Aerosol-based detection methods for HPLC in which HPLC effluent is converted to an aerosol and detected optically have been employed in the past. This paper describes a new aerosol-based detection method for HPLC, which we name aerosol charge detection. This detection method also involves generation of an aerosol but with aerosol detection by charging aerosol particles and measuring the current from the charged particle flux. A commercial electrical aerosol size analyzer was used for the aerosol detection. The constructed detector was tested using flow injection analysis with water as the mobile phase, and the signal response was found to be linear for sodium sulfate over the concentration ranges of 0.2-100 microg mL(-1) using one of the nebulizers. Minimum mass and concentration detection limits using the more efficient nebulizer were estimated to be 0.2 ng and 10 ng mL(-1), respectively. Behavior for most of the other compounds tested was similar with some differences in sensitivity. Testing the detector using reversed phase HPLC for glucose gave a range of linear response and detection limits that were similar to the flow injection analysis studies. Under most HPLC conditions, the noise will primarily be a function of solvent impurities; however, the electrical aerosol size analyzer allows the removal of small charged particles to improve the signal-to-noise ratio.     

聚酰亚胺驻极体的平均电荷重心迁移及电荷的贮存

本文利用开路 TSD 电流谱讨论了电晕充电期间热处理对聚酰亚胺薄膜驻极体电荷贮存稳定性的影响,分析了恒压电晕充电期间电荷的建立过程,研究了延长注极时间及在不同温度下电晕充电的聚酰亚胺薄膜沉积电荷平均深度向背电极的迁移规律。     

Measurement and Control of Triboelectrically Charged Silica and Glassy Carbon Particles

In this study, a particle trajectory analysis and charging measurements of triboelectrically charged silica and glassy carbon particles were conducted to investigate the effects of charging gas velocity and particle size on triboelectrical charging characteristics. A particle motion analysis system (PMAS) was used to measure charged particle motion information in the separation chamber with an applied uniform electric field, and the particle charging amount was calculated from the particle size and the electrostatic mobility was determined by the PMAS. The test system consisted of a particle generator, a spiral-type tribocharger made of a copper tube, and a particle motion analysis system to measure the particle size and velocity. The experiments were conducted with test particles of silica and glassy carbon and the average charging gas velocities of 6, 10, 15, 20 m/s to analyze the effect on particle charging. As a result, the silica and glassy carbon particles acquired negative and positive charges, respectively, due to the differences in the work functions, and the charging gas velocity effect on particle charge was approximately linear with an increasing velocity yielding a higher average particle charge and wider distribution.     

Measurement and Control of Triboelectrically Charged Silica and Glassy Carbon Particles

In this study, a particle trajectory analysis and charging measurements of triboelectrically charged silica and glassy carbon particles were conducted to investigate the effects of charging gas velocity and particle size on triboelectrical charging characteristics. A particle motion analysis system (PMAS) was used to measure charged particle motion information in the separation chamber with an applied uniform electric field, and the particle charging amount was calculated from the particle size and the electrostatic mobility was determined by the PMAS. The test system consisted of a particle generator, a spiral-type tribocharger made of a copper tube, and a particle motion analysis system to measure the particle size and velocity. The experiments were conducted with test particles of silica and glassy carbon and the average charging gas velocities of 6, 10, 15, 20 m/s to analyze the effect on particle charging. As a result, the silica and glassy carbon particles acquired negative and positive charges, respectively, due to the differences in the work functions, and the charging gas velocity effect on particle charge was approximately linear with an increasing velocity yielding a higher average particle charge and wider distribution.     

Chemical characterization of individual, airborne sub-10-nm particles and molecules

A nanoaerosol mass spectrometer (NAMS) is described for real-time characterization of individual airborne nanoparticles. The NAMS includes an aerodynamic inlet, quadrupole ion guide, quadrupole ion trap, and time-of-flight mass analyzer. Charged particles in the aerosol are drawn through the aerodynamic inlet, focused through the ion guide, and captured in the ion trap. Trapped particles are irradiated with a high-energy laser pulse to reach the "complete ionization limit" where each particle is thought to be completely disintegrated into atomic ions. In this limit, the relative signal intensities of the atomic ions give the atomic composition. The method is first demonstrated with sucrose particles produced with an electrospray generator. Under the conditions used, the particle detection efficiency (fraction of charged particles entering the inlet that are subsequently analyzed) reaches a maximum of 10(-4) at 9.5 nm in diameter and the size distribution of trapped particles has a geometric standard deviation of 1.1 based on a log-normal distribution. A method to deconvolute overlapping multiply charged ions (e.g. C3+ and O4+) is presented. When applied to sucrose spectra, the measured C/O atomic ratio is 1.1, which matches the expected ratio from the molecular formula. The spectra of singly charged bovine serum albumin (BSA) molecules are also presented, and the measured and expected C/N/O atomic ratios are within 15% of the each other. Also observed in the BSA spectra are signals from 13C and 32S which arise from 40 and approximately 34 atoms per molecule (particle), respectively. Potential applications of NAMS to atmospheric chemistry and biotechnology are briefly discussed.     

用于微机电系统的SiO2/Si3N4驻极体的制备及电荷稳定性

驻极体微型发电机是近期提出的微电子机械系统开发中的一个新领域,驻极体电荷稳定性则是影响驻极体微型发电机性能的关键.用等离子体增强化学气相沉积(PECVD)方法制备SiO2/ Si3N4双层膜,采用电晕充电和热极化方法对材料进行注极形成驻极体,探讨了器件加工工艺及存储环境对双层膜驻极体电荷稳定性的影响.结果表明,电晕充电后SiO2/ Si3N4双层膜的电荷存储稳定性明显优于SiO2单层膜;传统的电晕注极方法仅适用于大面积驻极体的制备,但对微米量级的材料表面不适用;微器件制备的工艺流程对驻极体电荷稳定性有显著影响,但存储环境对热极化驻极体电荷稳定性的影响很小.     

On a criterion of the appearance of an upward leader from ground-based objects

Results of an experimental study of processes forming an upward leader discharge from a grounded rod electrode in the electric field of an artificial cloud of charged water aerosol are presented. The transition of the streamer corona flash to an upward leader discharge was found to be of a probabilistic character and to be determined, first of all, not by the current amplitude, and not only by the flash charge passing through the stem of the pulse corona, but by a set of parameters: duration of the current passage at a rather high level and optimum value of the corona charge passed through the stem base. The range of radii of curvature of the rod-shaped lightning arrester tip (from 20 to 25 mm) at which the highest probability of the appearance of an upward leader is observed has been revealed.     

Particulate structures produced by electrosprays of colloidal silica suspensions in both negative and positive zeta potentials

Interaction between surface charge (zeta potential) of colloidal silica nanoparticles and the charge-induced droplets suspended in the gas phase by electrospray is investigated for the first time based on the particle physical (morphology, size, and size distribution) and optical properties. Colloidal silica nanoparticles having negative and positive zeta potential were subjected to electrospray in both negative and positive mode, and deposited on a substrate (silicon wafer). Visual observation of the substrate with particle deposition shows various white shades, corresponding to the changes in optical properties, as supported by the ultraviolet-visible–near-infrared spectroscopy. Microscopic analysis revealed the strong correlation between the colloid surface charge and charging mode (positive or negative) of the sprayed droplets to the particle morphology and size. The findings of the present study demonstrate the capability of the electrospray method to tune the physical and optical properties of colloidal silica nanoparticles with different surface charges.