Conventional Electrospray Research Articles

Characterization of water-soluble synthetic polymeric substances in wastewater using LC-HRMS/MS

Synthetic water-soluble polymeric materials are widely employed in e.g. cleaning detergents, personal care products, paints or textiles. Accordingly, these compounds reach sewage treatment plants and may enter receiving waters and the aquatic environment. Characteristically, these molecules show a polydisperse molecular weight distribution, comprising multiple repeating units, i.e. a homologous series (HS). Their analysis in environmentally relevant samples has received some attention over the last two decades, however, the majority of previous studies focused on surfactants and a molecular weight range <1000 Da. To capture a wider range on the mass versus polarity plane and extend towards less polar contaminants, a workflow was established using three different ionization strategies, namely conventional electrospray ionization, atmospheric pressure photoionization and atmospheric pressure chemical ionization. The data evaluation consisted of suspect screening of ca. 1200 suspect entries and a non-target screening of HS with pre-defined accurate mass differences using ca. 400 molecular formulas of repeating units of HS as input and repeating retention time shifts as HS indicator.To study the fate of these water-soluble polymeric substances in the wastewater treatment process, the different stages, i.e. after primary and secondary clarifier, and after ozonation followed by sand filtration, were sampled at a Swiss wastewater treatment plant. Remaining with two different ionization interfaces, ESI and APPI, in both polarities, a non-targeted screening approach led to a total number of 146 HS (each with a minimum number of 4 members), with a molecular mass of up to 1200 detected in the final effluent. Of the 146 HS, ca 15% could be associated with suspect hits and approximately 25% with transformation products of suspects. Tentative characterization or probable chemical structure could be assigned to almost half of the findings. In positive ionization mode various sugar derivatives with differing side chains, for negative mode structures with sulfonic acids, could be characterized. The number of detected HS decreased significantly over the three treatment stages. For HS detectable also in the biological and oxidative treatment stages, a change in HS distribution towards to lower mass range was often observed.

Spatial distribution of the dropless ESI charged particles at IMS entrance

An experimental study and comparison of spatial distributions of charged particles for conventional electrospray (ESI) and for dropless electrospray with a dynamic flow splitter of analyzed solution at atmospheric pressure and room temperature was carried out. Comparison of distributions shows that the characteristic regions of ion formation differ significantly. The obtained dropless electrospay spatial distributions are matched with inlet parameters of optimized transfer system of an ion mobility spectrometer (IMS) based on electrostatic focusing of the charged particles.

Characterization of RDX and HMX explosive adduct ions using ESI FT-ICR MS.

Investigation of two common explosives such as cyclonite (RDX) and cyclotetramethylenetetranitramine (HMX) using a mass spectrometer with ultrahigh resolution and accuracy has not been comprehensively performed. Here, ultrahigh mass accuracy 15-T Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) spectra were utilized to comprehensively characterize the adduct ions of RDX and HMX. Two different ionization sources such as a conventional electrospray ionization (ESI) source and a chip-based static nano-ESI source were used to investigate the adduct ions of RDX and HMX. The ESI-MS analyses of two explosives in negative ion mode provide some adduct ions of RDX and HMX even without prior addition of their corresponding anions. A total of six types of adduct ion were characterized: [M + Cl]- , [M + HCOO]- , [M + NO2 ]- , [M + CH3 COO]- , [M + NO3 ]- , and [M + C3 H5 O3 ]- , where M is either RDX or HMX. The ultrahigh accuracy of the 15-T FT-ICR MS was utilized to distinguish two closely spaced peaks representing the monoisotopic [M + NO2 ]- and second isotopic [M + HCOO]- ions, thereby enabling the discovery of a [M + NO2 ]- adduct ion in the ESI analysis of RDX or HMX. [M + NO2 ]- and [M + CH3 COO]- adduct ions were only observed when using a static nano-ESI source. It is the first report explaining the discovery of [M + NO2 ]- adduct ion in the ESI-MS analyses of RDX and HMX.

Acoustic Droplet Ejection and Open Port Interface for Rapid Analysis of Metabolic Stability Assays

In vitro absorption, distribution, metabolism and elimination (ADME) assays are widely used for profiling compounds in pharmaceutical drug discovery programs. Many compounds are screened in metabolic stability assays, using liver microsomes as a model of intrinsic hepatic clearance. Analysis of metabolic stability assays has relied on high throughput LC-MS/MS techniques to keep up with automated assays and compound profiling needs. An experimental alternative to sample analysis via fast chromatography employs an open port interface (OPI) which dilutes and directs acoustically-ejected droplets from microtiter plates to a conventional electrospray ion source for ionization and introduction into a mass spectrometer. Metabolic stability assays of 37 commercial drug compounds using in human, dog, rat and mouse liver microsomes (LMs), were analyzed by LC-MS/MS and an experimental breadboard version of an ADE-OPI-MS/MS system. Results from the experiments comparing intrinsic clearance (CLint) generated with ADE-OPI-MS/MS vs fast LC-MS/MS for all compounds showed ≥86% of CLint values were within a factor of two with R2 ≥ 0.86 using 25 nL and 5 nL sample ejection volumes on the ADE-OPI-MS/MS instrument. Throughput with the experimental ADE-OPI-MS/MS system used in this study was more than ten-fold faster than analysis by the fast LC-MS/MS at 1.3 s/sample versus 17.2 s/sample, respectively.

Triboelectric nanogenerators with porous and hierarchically structured silk fibroin films via water electrospray-etching technology

Abstract Triboelectric nanogenerator (TENG) has great potential applications in self-powered electronic devices, especially in flexible and wearable applications. Currently, to improve the performances, micro/nano structured surfaces are constructed in TENGs using complicated, costly, and toxic processes. Herein, a cost-effective and versatile water electrospray-etching (ESE) process for fabrication micro/nano structured silk fibroin (SF) triboelectric film has been presented. The water-soluble SF film could be easily dissolved by the atomized water droplets, meanwhile, as the residual charges on the droplets transferred and accumulated on to the SF surface, a patterned electrical field emerged due to the peak effect on the etched crater-like structures and manipulated the positions of deposition of the charged droplets. Our ESE strategy, which was different from the randomly distributed deposition by conventional electrospray deposition (ESD) process, could obtain quasi-periodical and porous structures, providing significantly increased surface roughness. The structural features, such as period and depth of the micropores, could be controlled by adjusting the spray parameters. The maximum output voltage and power density of the TENGs with porous structures were obviously increased by 180%, compared to 100 V obtained for a planar device. Furthermore, hierarchical micro/nano structures could be simply obtained by mixing SiO2 nanospheres in the aqueous precursor solution as nano-electrets. With this, the output voltage was up to 260 V, representing an overall 260% increase over the value of a planar device. The highest total power and peak power density were 0.65 mW and 161.5 μW/cm2 at a driving force of 18 N and frequency of 1 Hz. Meanwhile, the porous SF based TENG exhibited higher transmittance due to light scattering effects. The proposed water ESE strategy has advantages such as low cost, large area applications, bio-compatibility and nontoxicity, showing great promise as a technology in practical use.

Insights into the chemistry and structure of iron gall ink based on “two-step” bamboo nib-spray/mass spectrometry

A study of the dark-blue insoluble precipitate that makes up gall ink using bamboo nib-spray mass spectrometry (PS-MS) is described. A ferrous tannate complex is formed, i.e. an insoluble organic metal complex - iron gallate ink (IGI) is produced when tannin is mixed with iron sulfate. Since it is not possible to detect this IGI precipitate by conventional electrospray ionization (ESI) mass spectrometry, we report on an attempt to resolve this problem by a new method in this study in an. The method involved “two steps” using bamboo nib-spray/MS. A gallic acid solution was initially used as a model sample and the ESI mode was operated under a negative voltage. This approach permitted the optimized position between the spray-tip and the mass inlet (either distance or angle) to be determined. Following this, the ESI applied voltage was changed to positive and, at this moment, a ferrous sulfate solution was added to the spray-tip, both reactants are sprayed out immediately and are simultaneously ionized while a complex binding reaction occurs. This permits the IGI dark-blue insoluble precipitate to be ionized and detected. As a result, several specific peaks could be observed. The resulting m/z = 153, 225, 243, 431 peaks are assigned to [C7H5O4]+, [C7H5O5Fe]+, [C7H5O5Fe‧H2O]+, and [(C6H3O3) (C6H4O3)Fe2‧4H2O]+, respectively.

Imidazole Derivatives Improve Charge Reduction and Stabilization for Native Mass Spectrometry.

Noncovalent interactions between biomolecules are critical to their activity. Native mass spectrometry (MS) has enabled characterization of these interactions by preserving noncovalent assemblies for mass analysis, including protein-ligand and protein-protein complexes for a wide range of soluble and membrane proteins. Recent advances in native MS of lipoprotein nanodiscs have also allowed characterization of antimicrobial peptides and membrane proteins embedded in intact lipid bilayers. However, conventional native electrospray ionization (ESI) can disrupt labile interactions. To stabilize macromolecular complexes for native MS, charge reducing reagents can be added to the solution prior to ESI, such as triethylamine, trimethylamine oxide, and imidazole. Lowering the charge acquired during ESI reduces Coulombic repulsion that leads to dissociation, and charge reduction reagents may also lower the internal energy of the ions through evaporative cooling. Here, we tested a range of imidazole derivatives to discover improved charge reducing reagents and to determine how their chemical properties influence charge reduction efficacy. We measured their effects on a soluble protein complex, a membrane protein complex in detergent, and lipoprotein nanodiscs with and without embedded peptides, and used computational chemistry to understand the observed charge-reduction behavior. Together, our data revealed that hydrophobic substituents at the 2 position on imidazole can significantly improve both charge reduction and gas-phase stability over existing reagents. These new imidazole derivatives will be immediately beneficial for a range of native MS applications and provide chemical principles to guide development of novel charge reducing reagents.

An extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) for online measurement of atmospheric aerosol particles

Abstract. Real-time, online measurements of atmospheric organic aerosol (OA) composition are an essential tool for determining the emissions sources and physicochemical processes governing aerosol effects on climate and health. However, the reliance of current techniques on thermal desorption, hard ionization, and/or separated collection/analysis stages introduces significant uncertainties into OA composition measurements, hindering progress towards these goals. To address this gap, we present a novel, field-deployable extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF), which provides online, near-molecular (i.e., molecular formula) OA measurements at atmospherically relevant concentrations without analyte fragmentation or decomposition. Aerosol particles are continuously sampled into the EESI-TOF, where they intersect a spray of charged droplets generated by a conventional electrospray probe. Soluble components are extracted and then ionized as the droplets are evaporated. The EESI-TOF achieves a linear response to mass, with detection limits on the order of 1 to 10 ng m−3 in 5 s for typical atmospherically relevant compounds. In contrast to conventional electrospray systems, the EESI-TOF response is not significantly affected by a changing OA matrix for the systems investigated. A slight decrease in sensitivity in response to increasing absolute humidity is observed for some ions. Although the relative sensitivities to a variety of commercially available organic standards vary by more than a factor of 30, the bulk sensitivity to secondary organic aerosol generated from individual precursor gases varies by only a factor of 15. Further, the ratio of compound-by-compound sensitivities between the EESI-TOF and an iodide adduct FIGAERO-I-CIMS varies by only ±50 %, suggesting that EESI-TOF mass spectra indeed reflect the actual distribution of detectable compounds in the particle phase. Successful deployments of the EESI-TOF for laboratory environmental chamber measurements, ground-based ambient sampling, and proof-of-concept measurements aboard a research aircraft highlight the versatility and potential of the EESI-TOF system.

Internal Energy Deposition in Infrared Matrix-Assisted Laser Desorption Electrospray Ionization With and Without the Use of Ice as a Matrix.

The internal energy deposited into analytes during the ionization process largely influences the extent of fragmentation, thus the appearance of the resulting mass spectrum. The internal energy distributions of a series of para-substituted benzyl pyridinium cations in liquid and solid-state generated by infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) were measured using the survival yield method, of which results were subsequently compared with conventional electrospray ionization (ESI). The comparable mean internal energy values (e.g., 1.8-1.9eV at a collision energy of 15eV) and peak widths obtained with IR-MALDESI and ESI support that IR-MALDESI are essentially a soft ionization technique where analytes do not gain considerable internal energy during the laser-induced desorption process and/or lose energy during uptake into charged electrospray droplets. An unusual fragment ion, protonated pyridine, was only found for solid IR-MALDESI at relatively high collision energies, which is presumably resulted from direct ionization of the pre-charged analytes in form of salts. Analysis of tissue with an ice layer consistently yielded ion populations with higher internal energy than its counterpart without an ice layer, likely due to a substantially enhanced number of IR absorbers with ice. Further measurements with holo-myoglobin show that IR-MALDESI-MS retains the noncovalently bound heme-protein complexes under both native-like and denaturing conditions, while complete loss of the heme group occurred in denaturing ESI-MS, showing that the softness of IR-MALDESI is equivalent or superior to ESI for biomolecules.

Electrolyte solution-assisted electrospray deposition for direct coating and patterning of polymeric nanoparticles on non-conductive surfaces

Though electrospray deposition has significant impacts on various fields of energy, display, sensor, and biomedical engineering due to its strength in achieving functional coating or patterning of nano/microparticles on a substrate, most of the electrospray deposition techniques have been applicable only to electroconductive substrates, which limits the potential applications of the electrospray deposition. Here, we report a novel electrolyte solution-assisted electrospray deposition (ELED) process, which facilitates direct deposition of nano/microparticles on various substrates including a non-conductive surface. Beyond the direct surface coating, the ELED enabled to pattern nanoparticles on a selected micro-scale region on 2D flat and even 3D curved surfaces by simply modulating the surface wettability followed by selectively positioning electrolyte solution. Strikingly, the ELED showed the dramatic enhancement in the deposition efficiency of the electrosprayed particles on the non-conductive surface compared to conventional electrospray deposition process with a metal collector. The individual controllability of both the diameter of nanoparticles and the thickness of the deposited nanoparticle layer was achieved by adjusting the polymer concentration, the flow rate, the applied voltage, and electrospraying time. Lastly, we demonstrated one example of biomedical engineering applications of the ELED by patterning the NIH/3T3 fibroblasts and promoting alignment of C2C12 myoblasts on line patterns of cell-friendly polycarprolactone nanoparticles on a cell-repellent polydimethylsiloxane substrate.

Fabrication of a high-density emitter array for electrospray thrusters using field emitter array process

To improve the thrust density of electrospray thrusters using ionic liquids as the propellant, we have fabricated a high-density emitter array utilizing the fabrication technique of a field emitter array (FEA) or gated nano electron sources. The density of the emitter array can reach approximately 4 million cm−2, which is four orders of magnitude higher than that of conventional electrospray thrusters. Performing deep reactive ion etching from the back side of the same structure as FEAs and removing their Ni cones by dilute nitric acid, we have successfully fabricated sub-μm scale capillary emitters with self-aligned extractor electrodes and ionic liquid reservoirs behind them. Current measurements were also conducted with EMI-BF4 and EMI-DCA as the propellant. Although the ion was not extracted with EMI-BF4 owing to its electrochemical reaction with the electrodes, both positive and negative ion currents were detected using EMI-DCA, where the current density exceeded that of conventional electrospray thrusters.

Deep-ultraviolet laser ablation electrospray ionization mass spectrometry.

A 193-nm wavelength deep ultraviolet laser was used for ambient laser ablation electrospray ionization mass spectrometry of biological samples. A pulsed ArF excimer laser was used to ablate solid samples, and the resulting plume of the desorbed material merged with charged electrospray droplets to form ions that were detected with a quadrupole time-of-flight mass spectrometer. Solutions containing peptide and protein standards up to 66-kDa molecular weight were deposited on a metal target, dried, and analyzed. No fragmentation was observed from peptides and proteins as well as from the more easily fragmented vitamin B12 molecule. The mass spectra contained peaks from multiply charged ions that were identical to conventional electrospray. Deep UV laser ablation of tissue allowed detection of lipids from untreated tissue. The mechanism of ionization is postulated to involve absorption of laser energy by a fraction of the analyte molecules that act as a sacrificial matrix or by residual water in the sample.

Analyte‐substrate interactions at functionalized tip electrospray ionization mass spectrometry: Molecular mechanisms and applications

Conventional electrospray ionization mass spectrometry (ESI-MS) commonly uses capillary tip for sample introduction and ionization. In recent years, ESI-MS using noncapillary substrate tips has attracted growing interest as it allows separation and enrichment of analytes from complex samples due to analytes-substrate interactions. In this work, model mixtures and functionalized tips were employed to investigate the molecular mechanism of the analyte-substrate interactions. The mixtures were directly loaded on substrate tips, and then temporal responses of analytes were investigated by monitoring selected ion chromatogram (SIC) responses of each analyte. It is found that all analytes are sprayed out together when bulk solution loaded substrate surface and then sequential ionization of analytes were observed. Sequential ionization of analytes was affected by the analytes-substrate interactions which caused analytes of weaker-interaction to be faster moved and the analytes of stronger-interactions to be retained on the substrate. The main molecular mechanisms of analyte-substrate interactions were revealed to be hydrophobic interactions and electrostatic interactions. Furthermore, based on the mechanistic insights, functionalized tips were further applied for rapid extractive sampling of target analytes from complex samples with good analytical performances. Overall, this study on the mechanism and applications of analyte-substrate interactions is useful for understanding the fundamental principles and further developments of functionalized tip electrospray ionization (TESI).

Optimization and Application of Paper-Based Spray Ionization Mass Spectrometry for Analysis of Natural Organic Matter.

In this study, paper-based ionization techniques-paper spray ionization (PSI) and paper spray chemical ionization (PSCI)-were evaluated and applied for high-resolution mass spectrometry (MS)-based analysis of natural organic matter (NOM). Methanol:isopropyl alcohol (50:50, v/v) and ethanol emerged as good spray solvents for PSI, and hexane:dichloromethane (50:50, v/v) was a good spray solvent for PSCI. PSI-MS spectra could be obtained with NOM samples on the microgram scale, which is a critical advantage over conventional electrospray ionization (ESI)-MS when the amount of available sample is limited. In addition, PSI is more tolerant to salt contamination than ESI for NOM analysis. PSCI preferentially ionized less polar compounds, which may not be ionized well using ESI. Therefore, PSCI can be used as a complementary method to ESI or PSI. Comparison of the numbers of peaks obtained with ESI-, PSI-, and PSCI-MS showed that employing PSI and PSCI can increase the number of compounds that can be detected by high-resolution MS. In conclusion, the data presented in this study showed that PSI and PSCI are suitable ionization techniques for NOM analysis. To the best of our knowledge, this is the first study evaluating and applying PSI and PSCI for NOM analysis.

Simultaneous screening and quantification of aminoglycoside antibiotics in honey using mixed-mode liquid chromatography with quadrupole time-of-flight mass spectroscopy with heated electrospray ionization.

An analytical method based on liquid chromatography with quadrupole time-of-flight mass spectrometry has been developed for the simultaneous determination of six aminoglycoside antibiotics in honey. The sample pretreatment included extraction with aqueous trichloroacetic acid followed by solid-phase extraction on Strata-X polymeric reversed phase cartridges. Liquid chromatography separation was performed on an Obelisc R zwitterionic type mixed-mode column. An ionBooster™ heated electrospray source was used and showed enhanced ionization efficiency in comparison to a conventional electrospray source. The observed signal enhancement ranged from 3- (neomycin) to 16-fold (gentamicin C1). A data-dependent mass spectrometry acquisition approach was employed, in which the full mass spectrometry dataset provided quantification and a scheduled precursor list was used to trigger an alternating data-dependent acquisition of MS2 spectra for confirmation purposes. The described method was validated in accordance to CD 2002/657/EC. Decision limit values were in the range 11.2-33.6ng/g, and satisfactory performance characteristics were obtained for recovery (65-76%), repeatability (3.8-7.3%), and linearity (≥0.995). The method was applied to the analysis of 49 real honey samples from the country of Georgia. Streptomycin was detected in two samples at 117 and 35ng/g, and gentamicin C1 was detected in one sample at 32ng/g.

Direct Analysis of Proteins from Solutions with High Salt Concentration Using Laser Electrospray Mass Spectrometry.

The detection of lysozyme, or a mixture of lysozyme, cytochrome c, and myoglobin, from solutions with varying salt concentrations (0.1 to 250mM NaCl) is compared using laser electrospray mass spectrometry (LEMS) and electrospray ionization-mass spectrometry (ESI-MS). Protonated protein peaks were observed up to a concentration of 250mM NaCl in the case of LEMS. In the case of ESI-MS, a protein solution with salt concentration > 0.5mM resulted in predominantly salt-adducted features, with suppression of the protonated protein ions. The constituents in the mixture of proteins were assignable up to 250mM NaCl for LEMS and were not assignable above a NaCl concentration of 0.5mM for ESI. The average sodium adducts (<n>) bound to the 7+ charge state of lysozyme for LEMS measurements from salt concentrations of 2.5, 25, 50, and 100mM NaCl are 1.71, 5.23, 5.26, and 5.11, respectively. The conventional electrospray measurements for lysozyme solution containing salt concentrations of 0.1, 1, 2, and 5mM NaCl resulted in <n> of 2.65, 6.44, 7.57, and 8.48, respectively. LEMS displays an approximately two orders of magnitude higher salt tolerance in comparison with conventional ESI-MS. The non-equilibrium partitioning of proteins on the surface of the charged droplets is proposed as the mechanism for the high salt tolerance phenomena observed in the LEMS measurements. Graphical Abstract ᅟ.

Controlling of Electrospray Deposition for Micropatterns

Based on the electrohydrodynamic (EHD) theory, a novel method of near-field electrospray is proposed to fabricate micropatterns with micro/nano-scale particles. Compared with conventional electrospray technology, the deposition area can be decreased to print a regular pattern according to the moving trajectory of the substrate by shortening the distance between the nozzle and the collector to several millimeters in near-field electrospray. The controlling strategies in the near-field electrospray deposition process were investigated. The line width of printed pattern increased with the increase of applied voltage, deposition time, and flow rate of solution. However, it decreased with the increase of motion velocity of the substrate. By applying a suitable matching of electrospray parameters, the regular patterns with a line width under 500 μm were printed controllably on the substrate. Thereby, atomized particles from near-field electrospray were successfully deposited in specific patterns. Characters of ‘2’, ‘7’, and ‘9’ with uniform width and steady shape were patterned. This work provides an excellent way to promote the precision integrated manufacturing of electronic system.

Rapid characterization of nonpolar or low-polarity solvent extracts from herbal medicines by solvent-assisted electrospray ionization mass spectrometry.

The direct detection of nonpolar and low-polarity solvent extracts of herbal medicine is difficult by conventional electrospray ionization mass spectrometry (ESI-MS). This problem can be solved by solvent-assisted electrospray ionization mass spectrometry (SAESI-MS). With the help of assisted solvents (ESI-friendly solvents) at the tip of the spray needle, compounds (especially the low-polarity compounds) in nonpolar and low-polarity solvent extracts can be ionized directly. Herbal medicines were ultrasonically extracted with nonpolar or low-polarity solvents, such as petroleum ether. Thereafter, the extracts were analyzed by conventional ESI-MS, atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and SAESI-MS. The mass spectra obtained from these three methods were compared and analyzed. Unstable ion signals, and even no ion signals, were observed when the nonpolar and low-polarity solvent extracts were detected directly by conventional ESI-MS. Better specificity, higher sensitivity or cleaner spectra were acquired from SAESI-MS by comparing with the performance of conventional ESI-MS. The ion signals generated by SAESI-MS and APCI-MS were observed in clearly different m/z ranges. A variety of potential compounds were detected in the petroleum ether extracts of Pogostemon cablin and Ligusticum chuanxiong. The relative abundances and signal intensities of the same ion signals from the stems, leaves and decoction pieces of Pogostemon cablin were significantly different by SAESI-MS. As a convenient and efficient method, SAESI-MS can be used to directly detect compounds (especially the low-polarity compounds) in nonpolar or low-polarity solvent extracts of herbal medicines, providing abundant chemical information for pharmacological studies. SAESI-MS allows the simultaneous qualitative analysis of multiple compounds in the same complex samples and is thus particularly suitable for the preliminary screening of compounds in complex samples. SAESI-MS can be used to differentiate the different parts of herbal medicines.

Accelerated generation of (protonated) imines and quinoxalines by formation of C=N bonds in the microdroplets of a nebuliser.

Ions corresponding to protonated imines appear in the positive ion electrospray mass spectra of mixtures of the parent aromatic aldehyde and arylamine. The formation of these imine products occurs readily in the electrospray source nebuliser, even without the application of a spray potential. This accelerated formation of C=N bonds in the nebuliser has been extended to encompass the preparation of quinoxalines from a range of substituted phenylenediamines and benzils. The condensation may be induced either under conventional positive ion electrospray conditions (to give the protonated quinoxalines) or when the nebuliser is disconnected from the mass spectrometer (to give the neutral quinoxaline). Ions corresponding to intermediate adducts formed by condensation of the phenylenediamine component with the protonated benzil are observed in many cases when the condensation occurs in the mass spectrometer. This finding supports an interpretation based on nucleophilic addition in droplets generated by the nebuliser.

A hybrid aerodynamic and electrostatic atomization system for enhanced uniformity of thin film

Droplet deposition processes by the mechanisms of either aerodynamics or electrostatic spray have been widely studied in various applications such as aerosol generators, thin film coatings, and nanoparticle formations. Among the current state-of-art methodologies, air spray deposition can produce small-sized droplets without fine control on their sizes and uniformity in deposited thin films. Conventional electrospray depositions, on the other hand, can fabricate thin films with good uniform with a relatively slow deposition speed. In this paper, a hybrid mechanism by means of aerodynamic and electrostatic deposition is investigated and demonstrated to allow high throughput and improved uniformity for thin film depositions. It utilizes both the electrostatic force and aerodynamic force to atomize the liquid and control the droplet spraying process with good stability/repeatability. A uniform thin TiO2 film has been deposited as the demonstration example using this method. The velocities and trajectories of droplets during the deposition process have been characterized under different experimental parameters by using the technique of particle image velocimetry (PIV). This hybrid thin film fabrication method could be applicable in several industrial processes for better uniformity in making transparent electrodes, solar cells, displays, and automobiles.