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J P Borra - One of the best experts on this subject based on the ideXlab platform.
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review on water electro sprays and applications of charged drops with focus on the corona assisted cone jet mode for high efficiency air filtration by wet electro scrubbing of aerosols
Journal of Aerosol Science, 2018Co-Authors: J P BorraAbstract:Highlights: Electrosprays is a continuous production process of self-dispersed unipolar droplets with monodisperse/unimodal size distributions (0.2 99%) supports that Water ES in corona-assisted cone-jet could be applied to low cost Air cleaning Abstract: Electrospray of Water and aqueous solutions is a simple, steady and continuous process for the production of charged droplets. Applications of this low cost spraying process, easy to scale up and environment friendly with low water consumption are first presented. This review addresses the Electro-Spray (ES) in the cone-jet mode, with focus on water ES with or without discharges in ambient air. The physical constraints to achieve steady water electrospray in ambient air are depicted to account for Electro-Hydro-Dynamic equilibrium required for the cone and jet formation on the one hand and to control electrical discharges in the gas around the liquid (with continuous corona or without any discharge) on the other hand. Operating conditions and empirical scaling laws between regulation parameters (liquid flow rate and corona current) and the properties of droplets such as the size and the charge are presented for the corona-assisted cone-jet mode of water electrospray in air. Subsequent working conditions to achieve the other steady water ES, without discharge, are then justified. The interest of this corona assisted cone-jet mode of electrospray in air for the steady production of self-dispersed unipolar water droplets (close to the Rayleigh limit) with unimodal size distribution is presented with one environmental application for filtration by bipolar-scrubbing of suspended particles from exhaust or ambient aerosols, with lab-scale efficiencies of High Efficiency Particulate Air filters.
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Review on water electro-sprays and applications of charged drops with focus on the corona-assisted cone-jet mode for High Efficiency Air Filtration by wet electro-scrubbing of aerosols
Journal of Aerosol Science, 2018Co-Authors: J P BorraAbstract:Highlights: Electrosprays is a continuous production process of self-dispersed unipolar droplets with monodisperse/unimodal size distributions (0.2 < d modal < 150 µm) Applications of ES of aqueous solutions are reviewed with special attention for material production and bio-applications Means to achieve steady water ES are presented with respect to electrical discharges in ambient air around the liquid cone and jet Streamer discharges with transient and asymmetric space charges disrupt the EHD equilibrium for steady cone-jet mode, while the axisymmetric and quasi-stationary space charge is required to achieve steady water ES in the pulseless corona-assisted cone-jet mode Empirical scaling laws of droplet properties are reminded for both steady water ES in cone-jet with a pulseless corona and without discharge High filtration efficiencies of a lab-scale wet bipolar-scrubbers (>99%) supports that Water ES in corona-assisted cone-jet could be applied to low cost Air cleaning Abstract: Electrospray of Water and aqueous solutions is a simple, steady and continuous process for the production of charged droplets. Applications of this low cost spraying process, easy to scale up and environment friendly with low water consumption are first presented. This review addresses the Electro-Spray (ES) in the cone-jet mode, with focus on water ES with or without discharges in ambient air. The physical constraints to achieve steady water electrospray in ambient air are depicted to account for Electro-Hydro-Dynamic equilibrium required for the cone and jet formation on the one hand and to control electrical discharges in the gas around the liquid (with continuous corona or without any discharge) on the other hand. Operating conditions and empirical scaling laws between regulation parameters (liquid flow rate and corona current) and the properties of droplets such as the size and the charge are presented for the corona-assisted cone-jet mode of water electrospray in air. Subsequent working conditions to achieve the other steady water ES, without discharge, are then justified. The interest of this corona assisted cone-jet mode of electrospray in air for the steady production of self-dispersed unipolar water droplets (close to the Rayleigh limit) with unimodal size distribution is presented with one environmental application for filtration by bipolar-scrubbing of suspended particles from exhaust or ambient aerosols, with lab-scale efficiencies of High Efficiency Particulate Air filters.
Richard D. Smith - One of the best experts on this subject based on the ideXlab platform.
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Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures
Journal of The American Society for Mass Spectrometry, 2014Co-Authors: Ioan Marginean, Ryan T Kelly, Richard D. Smith, Keqi TangAbstract:Arrays of chemically etched emitters with individualized sheath gas capillaries were developed to enhance electrospray ionization (ESI) efficiency at subambient pressures. By incorporating the new emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, both ionization efficiency and ion transmission efficiency were significantly increased, providing enhanced sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses of conventional ESI-mass spectrometry (MS) interfaces by placing the emitter in the first reduced pressure region of the instrument. The new ESI emitter array design developed in this study allows individualized sheath gas around each emitter in the array making it possible to generate an array of uniform and stable Electrosprays in the subambient pressure (10 to 30 Torr) environment for the first time. The utility of the new emitter arrays was demonstrated by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared under different ESI source and interface configurations including a standard atmospheric pressure single ESI emitter/heated capillary, single emitter/SPIN and multi-emitter/SPIN configurations using an equimolar solution of nine peptides. The highest instrument sensitivity was observed using the multi-emitter/SPIN configuration in which the sensitivity increased with the number of emitters in the array. Over an order of magnitude MS sensitivity improvement was achieved using multi-emitter/SPIN compared with using the standard atmospheric pressure single ESI emitter/heated capillary interface. Graphical Abstract ᅟ
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Effect of pressure on electrospray characteristics.
Applied Physics Letters, 2009Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, Jason S Page, Richard D. SmithAbstract: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.
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Selection of the optimum electrospray voltage for gradient elution LC-MS measurements.
Journal of the American Society for Mass Spectrometry, 2008Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, Ronald J. Moore, David C. Prior, Brian L. Lamarche, Richard D. SmithAbstract:Changes in liquid composition during gradient elution liquid chromatography (LC) coupled to mass spectrometry (MS) analyses affect the electrospray operation. To establish methodologies for judicious selection of the electrospray voltage, we monitored in real time the effect of the LC gradient on the spray current. The optimum range of the electrospray voltage decreased as the concentration of organic solvent in the eluent increased during reversed-phase LC analyses. These results and related observations provided the means to rationally select the voltage to ensure effective electrospray operation throughout gradient-elution LC separations. For analyses in which the electrospray was operated at constant voltage, a small run-to-run variation in the spray current was observed, indicating a changing electric field resulting from fouling or degradation of the emitter. Algorithms using feedback from spray current measurements that can maintain the electrospray voltage within the optimum operating range throughout gradient elution LC-MS were evaluated. The electrospray operation with voltage regulation and at a constant, judiciously selected voltage during gradient elution LC-MS measurements produced data with similar reproducibility.
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Analytical Characterization of the Electrospray Ion Source in the Nanoflow Regime
Analytical chemistry, 2008Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, David C. Prior, Brian L. Lamarche, Richard D. SmithAbstract:A detailed characterization of a conventional low-flow electrospray ionization (ESI) source for mass spectrometry (MS) using solution compositions typical of reversed-phase liquid chromatography is reported. Contrary to conventional wisdom, the pulsating regime consistently provided better ESI-MS performance than the cone-jet regime for the interface and experimental conditions studied. This observation is supported by additional measurements showing that a conventional heated capillary interface affords more efficient sampling and transmission for the charged aerosol generated by a pulsating electrospray. The pulsating electrospray provided relatively constant MS signal intensities over a wide range of voltages, while the signal decreased slightly with increasing voltage for the cone-jet electrospray. The MS signal also decreased with increasing emitter−interface distance for both pulsating and cone-jet Electrosprays due to the expansion of the charged aerosol plume. At flow rates below 100 nL/min, the M...
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generation of multiple Electrosprays using microfabricated emitter arrays for improved mass spectrometric sensitivity
Analytical Chemistry, 2001Co-Authors: Keqi Tang, Yuehe Lin, Dean W Matson, Taeman Kim, Richard D. SmithAbstract:Arrays of microelectrospray emitters were fabricated on polycarbonate substrates using a laser etching technique. Stable multiElectrosprays were successfully generated in the liquid flow rate range relevant to mass spectrometric applications. Comparison of Electrosprays generated from the microfabricated emitter array and conventional fused-silica capillaries showed similar spray characteristics and reliability. Higher total electrospray ion currents were observed as the number of Electrosprays increased at a given total liquid flow rate. Consistent with the theoretical prediction, the total spray current at a constant total liquid flow rate was shown experimentally to be approximately proportional to the square root of the number of Electrosprays. It is further projected that when total flow rate is optimized the maximum achievable total current will be proportional to the number of emitters. Evaluation of the multielectrospray device using a triple quadrupole mass spectrometer showed a factor of 2-3 sensitivity enhancement for the spray numbers ranging from two to nine compared to a conventional single electrospray ionization source under the same operating conditions.
Kenzo Hiraoka - One of the best experts on this subject based on the ideXlab platform.
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Electrospray Generated from the Tip-Sealed Fine Glass Capillary Inserted with an Acupuncture Needle Electrode
Journal of The American Society for Mass Spectrometry, 2018Co-Authors: Dilshadbek T. Usmanov, Kenzo Hiraoka, Satoshi Ninomiya, Hiroshi Wada, Masaya Matsumura, Sachiyo Sanada-morimura, Hiroshi Nakano, Hiroshi NonamiAbstract:In electrospray, excess charges are supplied to a sample solution by the occurrence of electrochemical reactions. Recently, different versions of electrospray, e.g., dielectric barrier electrospray ionization, inductive desorption electrospray ionization, and electrostatic-ionization driven by dielectric polarization, have been reported in which the sample solution was not in direct contact with the metal electrode but separated by dielectric materials. The objective of the current work is to elucidate the mechanism of dielectric barrier electrospray. A sealed borosilicate glass capillary inserted with a fine acupuncture needle was used as a probe. A sample solution (~ 400 nL) was captured on the glass capillary tip and a positive high voltage (HV) pulse (+ 4.5 kV) was applied to the internal metal electrode. Mass spectra were measured as a function of the HV pulse width from μs to 10 s. Ions started to be detected with the pulse width of ~ 5 ms. The ion intensities increased slowly with time and reached a plateau in a few seconds. The charge distribution of cytochrome c [M + nH]^n+ shifted to higher n values from a few ms to seconds. In addition to cone-jet mode normal electrospray that lasted until all the liquid sample was depleted from the glass tip, the polarization-induced electrospray ionization was observed at the early stage of the HV application. Graphical Abstract ᅟ
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Relative secondary ion yields produced by vacuum-type electrospray droplet ion beams
Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials Processing Measurement and Phenomena, 2018Co-Authors: Satoshi Ninomiya, Lee Chuin Chen, Kenzo HiraokaAbstract:The relatively new electrospray droplet impact method is based on electrospray at atmospheric pressure and has been successful in achieving efficient desorption/ionization of biological molecules, soft etching of polymers, and nonselective etching of metal oxides. However, the beam current and brightness of this method are not practical for surface analyses. To improve the performance of this method, the authors have developed a new droplet ion beam gun using an electrospray of aqueous solutions in a vacuum. This technique could be expected to be a high-intensity massive cluster ion beam and they evaluate the performance of the vacuum-type electrospray droplet ion (V-EDI) gun. In this study, V-EDI and gas cluster ion beam guns were installed in a time-of-flight analyzer to directly compare the relative secondary ion yields of several biomolecules produced by several cluster ion beams.The relatively new electrospray droplet impact method is based on electrospray at atmospheric pressure and has been successful in achieving efficient desorption/ionization of biological molecules, soft etching of polymers, and nonselective etching of metal oxides. However, the beam current and brightness of this method are not practical for surface analyses. To improve the performance of this method, the authors have developed a new droplet ion beam gun using an electrospray of aqueous solutions in a vacuum. This technique could be expected to be a high-intensity massive cluster ion beam and they evaluate the performance of the vacuum-type electrospray droplet ion (V-EDI) gun. In this study, V-EDI and gas cluster ion beam guns were installed in a time-of-flight analyzer to directly compare the relative secondary ion yields of several biomolecules produced by several cluster ion beams.
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Electrospray droplet impact secondary ion mass spectrometry using a vacuum electrospray source.
Rapid communications in mass spectrometry : RCM, 2015Co-Authors: Riou Takaishi, Kenzo Hiraoka, Hiroshi Wada, Yuji Sakai, Satoshi Morita, Taiken Nakashima, Hiroshi NonamiAbstract:Rationale In electrospray droplet impact (EDI) developed in our laboratory, an atmospheric pressure electrospray source has been used. To increase the ion beam intensity and reduce the evacuation load, a vacuum electrospray cluster ion source using a silica capillary was developed. Methods A silica capillary with a tip inner diameter of 8 µm was used for vacuum electrospray using aqueous 10% methanol. To stabilize the flow rate of the liquid for nano-electrospray, a home-made constant pressure liquid pump was also developed. Results By using the silica tip nano-electrospray emitter and a constant pressure pump, stable electrospray with flow rate of 22 nL/min was realized without using any heating system such as laser irradiation. Comparative study of mass spectra obtained by atmospheric pressure EDI (A-EDI) and vacuum EDI (V-EDI) was made for various samples such as thermometer molecule, peptide, polystyrene, Alq3, NPD, C60, indium, and SiO2. V-EDI showed slightly milder ionization than A-EDI. Conclusions Because V-EDI gave higher target current (5–10 nA) than A-EDI (a few nA at most), V-EDI secondary ion mass spectrometry (SIMS) would be a useful technique for the surface and interface analysis. Copyright © 2015 John Wiley & Sons, Ltd.
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Development of a high‐performance electrospray droplet beam source
Surface and Interface Analysis, 2012Co-Authors: Satoshi Ninomiya, Lee Chuin Chen, Hiroaki Suzuki, Yuji Sakai, Kenzo HiraokaAbstract:The electrospray droplet impact (EDI) method was developed as a new massive cluster source, but the current EDI method lacks adequate beam focusing and density to achieve imaging and depth profiling with sufficient spatial resolution and within a reasonable time. To improve EDI beam performance, we have developed a technique for stable electrospraying of volatile liquids under vacuum. However, as is well known, vacuum electrospray of volatile liquids is extremely difficult because the evaporative cooling causes freezing of the volatile liquids in vacuum, and to prevent the freezing of these liquids, we irradiated the tip of the electrospray emitter with an infrared (10.6 µm) laser. The tip of the emitter was directly observed with optical microscopy, and the droplet ion beam current was measured with a Faraday cup. A stable vacuum electrospray of pure water was achieved with continuous laser irradiation. Also, typical modes of electrospray were clearly observed with the microscope even under vacuum conditions. The addition of 0.01 M trifluoroacetic acid to water caused an increase in current by at least one order of magnitude compared with water only. From these results, the vacuum electrospray technique can be expected to be a high-performance massive cluster ion beam source. Copyright © 2012 John Wiley & Sons, Ltd.
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Vacuum electrospray of volatile liquids assisted by infrared laser irradiation.
Rapid communications in mass spectrometry : RCM, 2012Co-Authors: Satoshi Ninomiya, Lee Chuin Chen, Hiroaki Suzuki, Yuji Sakai, Kenzo HiraokaAbstract:RATIONALE Current large cluster sources such as C60 or argon utilize gas-phase sources which are of low-brightness and cannot be focused efficiently to better than 1 micron diameter spot size. The development of a high-brightness large cluster ion source is of critical importance to achieve high resolution in secondary ion mass spectrometry (SIMS) imaging of organics. METHODS We propose a new high-brightness large cluster ion source, and a technique for producing a stable electrospray of volatile liquids under vacuum. It is known that vacuum electrospray of volatile liquids such as water is extremely difficult because of freezing of the liquids introduced in vacuum by evaporative cooling. To avoid freezing, the tip of the electrospray emitter was irradiated by a continuous wave infrared laser. RESULTS Without continuous laser irradiation the vacuum electrospray of a water/methanol solution was unstable with respect to the shapes of the Taylor cone and current, whereas continuous laser irradiation produced a stable electrospray of water. The typical modes of electrospray were clearly observed with an optical microscope even under vacuum conditions. A stable vacuum electrospray could be achieved by improving the vacuum pressure to suppress electric discharge and by using the laser to maintain the liquid state. CONCLUSIONS This is the first description of the production of a stable vacuum electrospray of volatile liquids such as water. This vacuum electrospray technique can be expected to produce a novel high-brightness large cluster ion beam source. Copyright © 2012 John Wiley & Sons, Ltd.
Keqi Tang - One of the best experts on this subject based on the ideXlab platform.
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Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures
Journal of The American Society for Mass Spectrometry, 2014Co-Authors: Ioan Marginean, Ryan T Kelly, Richard D. Smith, Keqi TangAbstract:Arrays of chemically etched emitters with individualized sheath gas capillaries were developed to enhance electrospray ionization (ESI) efficiency at subambient pressures. By incorporating the new emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, both ionization efficiency and ion transmission efficiency were significantly increased, providing enhanced sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses of conventional ESI-mass spectrometry (MS) interfaces by placing the emitter in the first reduced pressure region of the instrument. The new ESI emitter array design developed in this study allows individualized sheath gas around each emitter in the array making it possible to generate an array of uniform and stable Electrosprays in the subambient pressure (10 to 30 Torr) environment for the first time. The utility of the new emitter arrays was demonstrated by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared under different ESI source and interface configurations including a standard atmospheric pressure single ESI emitter/heated capillary, single emitter/SPIN and multi-emitter/SPIN configurations using an equimolar solution of nine peptides. The highest instrument sensitivity was observed using the multi-emitter/SPIN configuration in which the sensitivity increased with the number of emitters in the array. Over an order of magnitude MS sensitivity improvement was achieved using multi-emitter/SPIN compared with using the standard atmospheric pressure single ESI emitter/heated capillary interface. Graphical Abstract ᅟ
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Effect of pressure on electrospray characteristics.
Applied Physics Letters, 2009Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, Jason S Page, Richard D. SmithAbstract: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.
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Selection of the optimum electrospray voltage for gradient elution LC-MS measurements.
Journal of the American Society for Mass Spectrometry, 2008Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, Ronald J. Moore, David C. Prior, Brian L. Lamarche, Richard D. SmithAbstract:Changes in liquid composition during gradient elution liquid chromatography (LC) coupled to mass spectrometry (MS) analyses affect the electrospray operation. To establish methodologies for judicious selection of the electrospray voltage, we monitored in real time the effect of the LC gradient on the spray current. The optimum range of the electrospray voltage decreased as the concentration of organic solvent in the eluent increased during reversed-phase LC analyses. These results and related observations provided the means to rationally select the voltage to ensure effective electrospray operation throughout gradient-elution LC separations. For analyses in which the electrospray was operated at constant voltage, a small run-to-run variation in the spray current was observed, indicating a changing electric field resulting from fouling or degradation of the emitter. Algorithms using feedback from spray current measurements that can maintain the electrospray voltage within the optimum operating range throughout gradient elution LC-MS were evaluated. The electrospray operation with voltage regulation and at a constant, judiciously selected voltage during gradient elution LC-MS measurements produced data with similar reproducibility.
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Analytical Characterization of the Electrospray Ion Source in the Nanoflow Regime
Analytical chemistry, 2008Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, David C. Prior, Brian L. Lamarche, Richard D. SmithAbstract:A detailed characterization of a conventional low-flow electrospray ionization (ESI) source for mass spectrometry (MS) using solution compositions typical of reversed-phase liquid chromatography is reported. Contrary to conventional wisdom, the pulsating regime consistently provided better ESI-MS performance than the cone-jet regime for the interface and experimental conditions studied. This observation is supported by additional measurements showing that a conventional heated capillary interface affords more efficient sampling and transmission for the charged aerosol generated by a pulsating electrospray. The pulsating electrospray provided relatively constant MS signal intensities over a wide range of voltages, while the signal decreased slightly with increasing voltage for the cone-jet electrospray. The MS signal also decreased with increasing emitter−interface distance for both pulsating and cone-jet Electrosprays due to the expansion of the charged aerosol plume. At flow rates below 100 nL/min, the M...
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generation of multiple Electrosprays using microfabricated emitter arrays for improved mass spectrometric sensitivity
Analytical Chemistry, 2001Co-Authors: Keqi Tang, Yuehe Lin, Dean W Matson, Taeman Kim, Richard D. SmithAbstract:Arrays of microelectrospray emitters were fabricated on polycarbonate substrates using a laser etching technique. Stable multiElectrosprays were successfully generated in the liquid flow rate range relevant to mass spectrometric applications. Comparison of Electrosprays generated from the microfabricated emitter array and conventional fused-silica capillaries showed similar spray characteristics and reliability. Higher total electrospray ion currents were observed as the number of Electrosprays increased at a given total liquid flow rate. Consistent with the theoretical prediction, the total spray current at a constant total liquid flow rate was shown experimentally to be approximately proportional to the square root of the number of Electrosprays. It is further projected that when total flow rate is optimized the maximum achievable total current will be proportional to the number of emitters. Evaluation of the multielectrospray device using a triple quadrupole mass spectrometer showed a factor of 2-3 sensitivity enhancement for the spray numbers ranging from two to nine compared to a conventional single electrospray ionization source under the same operating conditions.
Ioan Marginean - One of the best experts on this subject based on the ideXlab platform.
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Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures
Journal of The American Society for Mass Spectrometry, 2014Co-Authors: Ioan Marginean, Ryan T Kelly, Richard D. Smith, Keqi TangAbstract:Arrays of chemically etched emitters with individualized sheath gas capillaries were developed to enhance electrospray ionization (ESI) efficiency at subambient pressures. By incorporating the new emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, both ionization efficiency and ion transmission efficiency were significantly increased, providing enhanced sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses of conventional ESI-mass spectrometry (MS) interfaces by placing the emitter in the first reduced pressure region of the instrument. The new ESI emitter array design developed in this study allows individualized sheath gas around each emitter in the array making it possible to generate an array of uniform and stable Electrosprays in the subambient pressure (10 to 30 Torr) environment for the first time. The utility of the new emitter arrays was demonstrated by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared under different ESI source and interface configurations including a standard atmospheric pressure single ESI emitter/heated capillary, single emitter/SPIN and multi-emitter/SPIN configurations using an equimolar solution of nine peptides. The highest instrument sensitivity was observed using the multi-emitter/SPIN configuration in which the sensitivity increased with the number of emitters in the array. Over an order of magnitude MS sensitivity improvement was achieved using multi-emitter/SPIN compared with using the standard atmospheric pressure single ESI emitter/heated capillary interface. Graphical Abstract ᅟ
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Effect of pressure on electrospray characteristics.
Applied Physics Letters, 2009Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, Jason S Page, Richard D. SmithAbstract: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.
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Selection of the optimum electrospray voltage for gradient elution LC-MS measurements.
Journal of the American Society for Mass Spectrometry, 2008Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, Ronald J. Moore, David C. Prior, Brian L. Lamarche, Richard D. SmithAbstract:Changes in liquid composition during gradient elution liquid chromatography (LC) coupled to mass spectrometry (MS) analyses affect the electrospray operation. To establish methodologies for judicious selection of the electrospray voltage, we monitored in real time the effect of the LC gradient on the spray current. The optimum range of the electrospray voltage decreased as the concentration of organic solvent in the eluent increased during reversed-phase LC analyses. These results and related observations provided the means to rationally select the voltage to ensure effective electrospray operation throughout gradient-elution LC separations. For analyses in which the electrospray was operated at constant voltage, a small run-to-run variation in the spray current was observed, indicating a changing electric field resulting from fouling or degradation of the emitter. Algorithms using feedback from spray current measurements that can maintain the electrospray voltage within the optimum operating range throughout gradient elution LC-MS were evaluated. The electrospray operation with voltage regulation and at a constant, judiciously selected voltage during gradient elution LC-MS measurements produced data with similar reproducibility.
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Analytical Characterization of the Electrospray Ion Source in the Nanoflow Regime
Analytical chemistry, 2008Co-Authors: Ioan Marginean, Keqi Tang, Ryan T Kelly, David C. Prior, Brian L. Lamarche, Richard D. SmithAbstract:A detailed characterization of a conventional low-flow electrospray ionization (ESI) source for mass spectrometry (MS) using solution compositions typical of reversed-phase liquid chromatography is reported. Contrary to conventional wisdom, the pulsating regime consistently provided better ESI-MS performance than the cone-jet regime for the interface and experimental conditions studied. This observation is supported by additional measurements showing that a conventional heated capillary interface affords more efficient sampling and transmission for the charged aerosol generated by a pulsating electrospray. The pulsating electrospray provided relatively constant MS signal intensities over a wide range of voltages, while the signal decreased slightly with increasing voltage for the cone-jet electrospray. The MS signal also decreased with increasing emitter−interface distance for both pulsating and cone-jet Electrosprays due to the expansion of the charged aerosol plume. At flow rates below 100 nL/min, the M...
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Astable regime in Electrosprays.
Physical Review E, 2007Co-Authors: Ioan Marginean, Peter Nemes, Akos VertesAbstract:Astable regimes are common in nonlinear systems ranging from electrooptic devices to cardiac rhythms under environmental stress. Electrosprays exhibit three main axial regimes (dripping, pulsating, and cone-jet). It is generally accepted that the transition between the pulsating and cone-jet regimes is sudden, accompanied by an abruptly enhanced spray current. Here we present an alternative to this scenario, in which the electrospray follows a new chaotic astable path to the cone-jet regime. The astable regime could be explained as a result of transitions between a limit cycle (pulsating regime) and a fixed point (cone-jet regime) in a subcritical Andronov-Hopf bifurcation due to small external perturbations (noise). With the introduction of this regime, a broader view of the diverse axial regimes becomes possible based on nonlinear dynamics that enables their consistent classification.