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Kenneth R Marcus - One of the best experts on this subject based on the ideXlab platform.
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monochromatic spatial imaging of the liquid sampling atmospheric pressure glow discharge effects of Gas flow on spatial profiles of analyte and background species
Spectrochimica Acta Part B: Atomic Spectroscopy, 2019Co-Authors: Katja A Hall, Htoo W Paing, Michael R Webb, Kenneth R MarcusAbstract:Abstract The liquid sampling – atmospheric pressure glow discharge (LS-APGD) microplasma was paired with a monochromatic imaging spectrometer (MIS) to interrogate relevant plasma species/elements. The coupling of the LS-APGD source to the MIS allows for the generation of spatial emission profiles at specific analyte and background species' wavelengths. A major goal of this work was to utilize these emission profiles to gain an understanding of the species' location in the plasma as well as the effects of plasma Gas flow on these emission profiles. It was found that as Sheath Gas and counter Gas flow rates were increased, there were visible differences in intensity and distribution of emission from the monitored species in the plasma. Silver was used as the representative (test) analyte for this work due to its good sensitivity, wavelength positioning, and ability to provide continuity for comparison to previous works. The majority of analyte emission was found to occur at the tip of the solution electrode, where solutes are introduced to the plasma, whereas various background species emitted throughout the plasma. In addition to aiding in the understanding of plasma operation based on spatial emission characteristics, these studies also aided in optimizing the Gas flow parameters for analyte emission intensity, signal-to-background (S/B), and signal-to-noise (S/N) values. The optimized Gas flow parameters were found to be 0.7 and 0.1 L min−1 for the Sheath and counter Gas respectively.
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evaluation of the operating parameters of the liquid sampling atmospheric pressure glow discharge ls apgd ionization source for elemental mass spectrometry
Analytical and Bioanalytical Chemistry, 2014Co-Authors: Lynn X Zhang, Benjamin T Manard, Stefanie Konegger Kappel, Kenneth R MarcusAbstract:The liquid sampling-atmospheric pressure glow discharge (LS-APGD) has been assessed as an ionization source for elemental analysis with an interdependent, parametric evaluation regarding Sheath/cooling Gas flow rate, discharge current, liquid flow rate, and the distance between the plasma and the sampling cone of the mass spectrometer. In order to better understand plasma processes (and different from previous reports), no form of collision/reaction processing was performed to remove molecular interferents. The evaluation was performed employing five test elements: cesium, silver, lead, lanthanum and nickel (10−4 mol L−1 in 1 mol L−1 HNO3). The intensity of the atomic ions, levels of spectral background, the signal-to-background ratios, and the atomic-to-oxide/hydroxide adduct ratios were monitored in order to obtain fundamental understanding with regards to not only how each parameter effects the performance of this LS-APGD source, but also the inter-parametric effects. The results indicate that the discharge current and the liquid sampling flow rates are the key aspects that control the spectral composition. A compromise set of operating conditions was determined: Sheath Gas flow rate = 0.9 L min−1, discharge current = 10 mA, solution flow rate = 10 μL min−1, and sampling distance = 1 cm. Limits of detection (LODs) were calculated using the SBR-RSDB (signal-to-background ratio/relative standard deviation of the background) approach under the optimized condition. The LODs for the test elementals ranged from 15 to 400 ng mL−1 for 10 μL injections, with absolute mass values from 0.2 to 4 ng.
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liquid sampling atmospheric pressure glow discharge ls apgd ionization source for elemental mass spectrometry preliminary parametric evaluation and figures of merit
Analytical and Bioanalytical Chemistry, 2012Co-Authors: Derrick C Quarles, Anthony J Carado, Charles J Barinaga, David W Koppenaal, Kenneth R MarcusAbstract:A new, low-power ionization source for the elemental analysis of aqueous solutions has recently been described. The liquid sampling–atmospheric pressure glow discharge (LS-APGD) source operates at relatively low currents (<20 mA) and solution flow rates (<50 μL min−1), yielding a relatively simple alternative for atomic mass spectrometry applications. The LS-APGD has been interfaced to what is otherwise an organic, LC-MS mass analyzer, the Thermo Scientific Exactive Orbitrap without any modifications, other than removing the electrospray ionization source supplied with that instrument. A glow discharge is initiated between the surface of the test solution exiting a glass capillary and a metallic counter electrode mounted at a 90° angle and separated by a distance of ~5 mm. As with any plasma-based ionization source, there are key discharge operation and ion sampling parameters that affect the intensity and composition of the derived mass spectra, including signal-to-background ratios. We describe here a preliminary parametric evaluation of the roles of discharge current, solution flow rate, argon Sheath Gas flow rate, and ion sampling distance as they apply on this mass analyzer system. A cursive evaluation of potential matrix effects due to the presence of easily ionized elements indicate that sodium concentrations of up to 50 μg mL−1 generally cause suppressions of less than 50%, dependant upon the analyte species. Based on the results of this series of studies, preliminary limits of detection (LOD) have been established through the generation of calibration functions. While solution-based concentration LOD levels of 0.02–2 μg mL−1 are not impressive on the surface, the fact that they are determined via discrete 5 μL injections leads to mass-based detection limits at picogram to single-nanogram levels. The overhead costs associated with source operation (10 W d.c. power, solution flow rates of <50 μL min−1, and Gas flow rates <10 mL min−1) are very attractive. While further optimization in the source design is suggested here, it is believed that the LS-APGD ion source may present a practical alternative to inductively coupled plasma sources typically employed in elemental mass spectrometry.
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role of powering geometries and Sheath Gas composition on operation characteristics and the optical emission in the liquid sampling atmospheric pressure glow discharge
Spectrochimica Acta Part B: Atomic Spectroscopy, 2002Co-Authors: Clay W Davis, Kenneth R MarcusAbstract:Abstract Characterization of the liquid sampling-atmospheric pressure glow discharge optical emission spectroscopy (LS-APGD-OES) source is described with regards to applications in low-flow separations such as capillary liquid chromatography and electrophoresis. Four powering modes are investigated, including the effects of the individual modes on current–voltage characteristics, analyte emission response, and temporal broadening of flow injection profiles. A concentric Sheath Gas is employed to stabilize the solution delivery at low liquid flow rates. Sheath Gas composition (N2 or He) effects analyte emission responses as well as Gas phase rotational and excitation temperatures. The respective powering modes both measures of temperature, with the OH rotational Gas temperatures ranging from ∼2100 to 3000 K and the Fe (I) excitation temperatures ranging from ∼2400 to 3600 K. Rotational temperature values increase slightly when helium is employed as a Sheath Gas as opposed to nitrogen, with the corresponding excitation temperatures increasing somewhat as well. Analytical response curves for Na and Hg in the various powering modes demonstrate good linearity, with the limits of detection for the analytes found to be on the order of ∼4–10 ppm for 5 μl injections; equating to absolute detection limits of between 20 and 45 ng. It is believed that the approach demonstrated here suggests further improvements that will permit applications in a wide variety of aqueous solution analyses where low-flow rates and limited volumes are encountered.
Gaofeng Zheng - One of the best experts on this subject based on the ideXlab platform.
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Three-dimensional composite electrospun nanofibrous membrane by multi-jet electrospinning with Sheath Gas for high-efficiency antibiosis air filtration.
Nanotechnology, 2021Co-Authors: Jiaxin Jiang, Zungui Shao, Xiang Wang, Ping Zhu, Deng Shiqing, Gaofeng ZhengAbstract:Three-dimensional (3D) composite polyvinylidene fluoride (PVDF) / polyacrylonitrile (PAN) electrospun nanofibrous membrane combining both thick and thin nanofibers have been fabricated by the method of multi-jet electrospinning with Sheath Gas to realize the high-efficiency air filtration under a low pressure drop. The thin PAN nanofibers form a dense membrane, with a strong capturing ability on the ultra-fine particles, while the thick PVDF nanofibers play a 3D supporting effect on the thin PAN nanofibers. In this case, this combination results in a fluffy membrane with higher porosity, which could achieve the airflow passing through the membrane without the air pressure drop. The effects of composite manner of thick nanofibers and thin nanofibers are investigated, in order to optimize the air filtration performance of 3D composite nanofibrous membrane. As a result, the maximum quality factor for air filtration could reach up to 0.398 Pa-1. The particle-fiber interaction model was used to simulate the air filtration process as well, and the simulation results were in fairly consistent with the experimental results, providing a guidance method for the optimization of composite nanofibrous membrane for high-efficiency air filtration. More interestingly, a cationic poly[2-(N,N-dimethyl amino) ethyl methacrylate] (PDMAEMA) was added in the PVDF solution to obtain a composite air filtration membrane with excellent antibiosis performance, which achieved the highest inhibition rate of approximately 90%. In short, this work provides an effective way to promote antibiosis air filtration performance by using electrospun nanofibrous membrane, while might effectively accelerate the biological protection application of current air filtration membrane.
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nanofiber membranes by multi jet electrospinning arranged as arc array with Sheath Gas for electrodialysis applications
Materials & Design, 2020Co-Authors: Gaofeng Zheng, Jiaxin Jiang, Xiang Wang, Juan Liu, Liwei LinAbstract:Abstract Multi-jet electrospinning arranged in an arc array with Sheath Gas has been developed for the high-efficiency production of nanofiber membranes. The arc array constrains the electric field interferences among multiple nozzles and the Sheath Gas in laminar flow overcomes the electric repulsive force among the jets. The stretching and focusing effect from the Sheath Gas reduces both the nanofiber diameter and the diameter range, which helps to realize the continuous stable multi-jet electrospinning to fabricate uniform nanofiber membranes. After the treatment of 98% concentrated sulfuric acid for the reactive exchange groups and a hot-pressing process, the membrane is then applicable to electrodialysis applications. Thanks to the net structure, there are many ion transmission passageways within the membrane, leading to the low membrane resistance and high ion transmission efficiency. Experimentally, the increase of membrane thickness results in the decrease of porosity, ion exchange capacity (IEC) and selective permeability and the increase in membrane resistance. The electrodialysis tests show good ion selection performance with a high desalinization ratio of NaCl solution.
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electrospinning jet behaviors under the constraints of a Sheath Gas
AIP Advances, 2016Co-Authors: Yang Zhao, Jiaxin Jiang, Xiang Wang, Ping Zhu, Kai Zhang, Gaofeng ZhengAbstract:Increasing the ejection efficiency and uniformity of nanofibers is the key to applications of electrospinning technology. In this work, a novel electrospinning spinneret with a Sheath Gas passageway is designed. The frictional resistance that stems from the Sheath Gas provides additional stretching and restriction forces on the jet. The Sheath Gas also reduces interference and enhances the stability of the charged jet. A bead-on-strain simulation model is built up to determine the constraint effects of the Sheath Gas. Simulation results show that the Sheath Gas decreases the motion area and increases the stretching ratio of the liquid jet. The stretching force from the Sheath Gas decreases the diameter and increases the uniformity of the nanofiber. As the Gas pressure increases from 0 kPa to 50 kPa, the critical voltage of the jet ejection decreases from 8.4 kV to 2.5 kV, the diameter of the nanofiber deposition zone decreases from 40 cm to 10 cm, and the diameter of the nanofibers decreases from 557.97 nm to 277.73 nm. The uniformity of nanofibers can be improved significantly using a Sheath Gas. The Sheath Gas contributes to the rapid deposition of a uniform nanofibrous membrane and the industrial applications of electrospinning.
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multi spinnerets electrospinning with assistant Sheath Gas
Nano Micro Engineered and Molecular Systems, 2014Co-Authors: Yihong Lin, Gaofeng Zheng, Weiwei Huang, Mingfeng Zhuang, Yongqiang Hong, Daoheng SunAbstract:Conference Name:9th IEEE International Conference on Nano/Micro Engineered and Molecular Systems, IEEE-NEMS 2014. Conference Address: Waikiki Beach, HI, United states. Time:April 13, 2014 - April 16, 2014.
Renato Zenobi - One of the best experts on this subject based on the ideXlab platform.
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On the mechanism of extractive electrospray ionization (EESI) in the dual-spray configuration
Analytical and Bioanalytical Chemistry, 2012Co-Authors: Rui Wang, Arto Juhani Gröhn, Rolf Dietiker, Detlef Gunther, Karsten Wegner, Renato ZenobiAbstract:Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet–droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet–droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet–droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the Sheath Gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet–droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be
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on the mechanism of extractive electrospray ionization eesi in the dual spray configuration
Analytical and Bioanalytical Chemistry, 2012Co-Authors: Rui Wang, Arto Juhani Gröhn, Rolf Dietiker, Detlef Gunther, Karsten Wegner, Renato ZenobiAbstract:Dual-spray extractive electrospray ionization (EESI) mass spectrometry as a versatile analytical technique has attracted much interest due to its advantages over conventional electrospray ionization (ESI). The crucial difference between EESI and ESI is that in the EESI process, the analytes are introduced in nebulized form via a neutral spray and ionized by collisions with the charged droplets from an ESI source formed by spraying pure solvent. However, the mechanism of the droplet–droplet interactions in the EESI process is still not well understood. For example, it is unclear which type of droplet–droplet interaction is dominant: bounce, coalescence, disruption, or fragmentation? In this work, droplet–droplet interaction was investigated in detail based on a theoretical model. Phase Doppler anemometry (PDA) was employed to investigate the droplet behavior in the EESI plume and provide the experimental data (droplet size and velocity) necessary for theoretical analysis. Furthermore, numerical simulations were performed to clarify the influence of the Sheath Gas flow on the EESI process. No coalescence between the droplets in the ESI spray and the droplets in the sample spray was observed using various geometries and sample flow rates. Theoretical analysis, together with the PDA results, suggests that droplet fragmentation may be the dominant type of droplet–droplet interaction in the EESI. The interaction time between the ESI droplet and the sample droplet was estimated to be <5 μs. This work gives a clear picture of droplet–droplet interactions in the dual-spray EESI process and detailed information for the optimization of this method for future applications that require higher sensitivity.
Ian A Blair - One of the best experts on this subject based on the ideXlab platform.
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liquid chromatography electron capture atmospheric pressure chemical ionization mass spectrometry analysis of pentafluorobenzyl derivatives of biomolecules and drugs in the attomole range
Analytical Chemistry, 2000Co-Authors: Gurkeerat Singh, Alejandro Gutierrez, Ian A BlairAbstract:The corona discharge used to generate positive and negative ions under conventional atmospheric pressure chemical ionization conditions also provides a source of Gas-phase electrons. This is thought to occur by displacement of electrons from the nitrogen Sheath Gas. Therefore, suitable analytes can undergo electron capture in the Gas phase in a manner similar to that observed for Gas chromatography/electron capture negative chemical ionization/mass spectrometry. This technique, which has been named electron capture atmospheric pressure chemical ionization/mass spectrometry, provided an increase in sensitivity of 2 orders of magnitude when compared with conventional atmospheric pressure chemical ionization methodology. It is a simple procedure to tag many biomolecules and drugs with an electron-capturing group such as the pentafluorobenzyl moiety before analysis. Pentafluorobenzyl derivatives have previously been used as electron capturing derivatives because they undergo dissociative electron capture in the Gas phase to generate negative ions through the loss of a pentafluorobenzyl radical. A similar process was found to occur under electron capture atmospheric pressure chemical ionization conditions. By monitoring the negative ions that were formed, it was possible to obtain attomole sensitivity for pentafluorobenzyl derivatives of a representative steroid, steroid metabolite, prostaglandin, thromboxane, amino acid, and DNA-adduct.
Lynn X Zhang - One of the best experts on this subject based on the ideXlab platform.
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evaluation of the operating parameters of the liquid sampling atmospheric pressure glow discharge ls apgd ionization source for elemental mass spectrometry
Analytical and Bioanalytical Chemistry, 2014Co-Authors: Lynn X Zhang, Benjamin T Manard, Stefanie Konegger Kappel, Kenneth R MarcusAbstract:The liquid sampling-atmospheric pressure glow discharge (LS-APGD) has been assessed as an ionization source for elemental analysis with an interdependent, parametric evaluation regarding Sheath/cooling Gas flow rate, discharge current, liquid flow rate, and the distance between the plasma and the sampling cone of the mass spectrometer. In order to better understand plasma processes (and different from previous reports), no form of collision/reaction processing was performed to remove molecular interferents. The evaluation was performed employing five test elements: cesium, silver, lead, lanthanum and nickel (10−4 mol L−1 in 1 mol L−1 HNO3). The intensity of the atomic ions, levels of spectral background, the signal-to-background ratios, and the atomic-to-oxide/hydroxide adduct ratios were monitored in order to obtain fundamental understanding with regards to not only how each parameter effects the performance of this LS-APGD source, but also the inter-parametric effects. The results indicate that the discharge current and the liquid sampling flow rates are the key aspects that control the spectral composition. A compromise set of operating conditions was determined: Sheath Gas flow rate = 0.9 L min−1, discharge current = 10 mA, solution flow rate = 10 μL min−1, and sampling distance = 1 cm. Limits of detection (LODs) were calculated using the SBR-RSDB (signal-to-background ratio/relative standard deviation of the background) approach under the optimized condition. The LODs for the test elementals ranged from 15 to 400 ng mL−1 for 10 μL injections, with absolute mass values from 0.2 to 4 ng.