Sheath Gas Research Articles

Flow and temperature patterns in an inductively coupled plasma reactor: Experimental measurements and CFD simulations

Measurements of temperature patterns in an inductively coupled plasma (ICP) have been carried out experimentally. Plasma torch was operated at different RF powers in the range of 3–14 kW at near atmospheric pressure and over a wide range of sheath gas flow rate (3–25 lpm). Measurements were made at five different axial positions in ICP torch. The chordal intensities were converted into a radial intensity profile by Abel Inversion technique. Typical radial temperature profile shows an off‐axis temperature peak, which shifts toward the wall as the power increases. Temperatures in the range of 6000–14,000 K were recorded by this method. The temperature profiles in the plasma reactor were simulated using computational fluid dynamics (CFD). A good agreement was found between the CFD predictions of the flow and temperature pattern with those published in the literature as well as the temperature profiles measured in the present work. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3647–3664, 2014

Evaluation of the operating parameters of the liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source for elemental mass spectrometry.

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.

RF 유도결합 열 플라즈마를 이용한 암모니아와 질소분위기에서 고순도 AlN 나노 분말의 합성

High-purity aluminum nitride nanopowders were synthesized using an RF induction thermal plasma instrument. Ammonia and nitrogen gases were used as sheath gas to control the reactor atmosphere. Synthesized AlN nanopowders were characterized by XRD, SEM, TEM, EDS, BET, FTIR, and N-O analyses. It was possible to synthesize high-purity AlN nanoparticles through control of the ammonia gas flow rate. However, additional process parameters such as plasma power and reactor pressure had to be controlled for the production of high-purity AlN nanopowders using nitrogen gas.

On-line reaction monitoring and mechanistic studies by mass spectrometry: Negishi cross-coupling, hydrogenolysis, and reductive amination.

Reaction monitoring using inductive ESI mass spectrometry allows chemical reactions to be tracked in real time, including air- and moisture-sensitive as well as heterogeneous reactions. Highly concentrated solutions can also be monitored for long periods without emitter clogging. Sheath gas assists in nebulization and a sample splitter reduces the delay time and minimizes contamination of the instrument. Short-lived intermediates (ca. 5 s) were observed in Pd/C-catalyzed hydrogenolysis, and several intermediates were seen in Negishi cross-coupling reactions.

On-Line Reaction Monitoring and Mechanistic Studies by Mass Spectrometry: Negishi Cross-Coupling, Hydrogenolysis, and Reductive Amination

Reaction monitoring using inductive ESI mass spectrometry allows chemical reactions to be tracked in real time, including air- and moisture-sensitive as well as heterogeneous reactions. Highly concentrated solutions can also be monitored for long periods without emitter clogging. Sheath gas assists in nebulization and a sample splitter reduces the delay time and minimizes contamination of the instrument. Short-lived intermediates (ca. 5 s) were observed in Pd/C-catalyzed hydrogenolysis, and several intermediates were seen in Negishi cross-coupling reactions.

Improving the Sensitivity of Mass Spectrometry by Using a New Sheath Flow Electrospray Emitter Array at Subambient Pressures

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.

유도결합 열 플라즈마를 이용한 고순도 질화알루미늄 나노 분말 합성

질화알루미늄(AlN)은 뛰어난 열적, 전기절연성 특성을 갖고 있어 반도체 기판용 재료나 전자 패키징 재료로 주목받고 있다. 질화알루미늄은 소결온도가 높고 불순물로 인한 물성저하 때문에 고순도화 및 나노원료화가 필수적이다. 본 연구에서는 RF 유도결합 열플라즈마를 이용하여 알루미늄 분말로부터 고순도의 질화알루미늄 나노분말을 합성하였다. Sheath gas로 사용된 암모니아의 유량 제어를 통해 고순도의 질화알루미늄 나노분말이 합성되는 조건을 확립하고자 하였으며 합성된 분말은 XRD, SEM, TEM, BET, FTIR, N-O분석을 통해 특성분석을 진행하였다. Aluminum nitride, which has outstanding properties such as high thermal conductivity and electrical resistivity, has been received a great attention as a substrate and packaging material of semiconductor devices. Since aluminum nitride has a high sintering temperature of 2173 K and its properties depends on the impurity level, it is necessary to synthesize high-purity and nano-sized aluminum nitride powders for the applications. In this research, we synthesized high purity aluminum nitride nanopowders from aluminum using RF induction thermal plasma system. Sheath gas (NH3) flow was controlled to establish the synthesis condition of high purity aluminum nitride nanopowders. The obtained aluminum nitride nanopowders were evaluated by XRD, SEM, TEM, BET, FTIR and N-O analysis.

Increasing the Performance of Portable Ion Mobility Analyzers: Development of the Periodic Focusing Differential Mobility Analyzer (PFDMA).

Ion mobility spectrometry (IMS) as a stand-alone technique has become increasingly important for applications in security, defense, and environmental monitoring, and also in biological applications such as molecular structure and -omic analysis when combined with mass spectrometry. Yet, the majority of these devices are drift cell based and limited by low duty cycles because of ion gating. Differential Mobility Analyzers (DMAs) are attractive alternatives due to their continuous ion transmission and success in analyzing aerosol particles in real time environmental tests. But, the resolution of a DMA is low due to difficulties in achieving laminar gas flow, low sample gas flow to sheath gas flow ratio, and high velocity sheath gas using small pumps, if portability is a concern. To overcome these challenges, we will introduce a new ion mobility spectrometer that increases the amount of work done on the ions during separation by introducing an electric field opposing the gas flow direction while simultaneously preserving laminar gas flow. The development of the Periodic Focusing Differential Mobility Analyzer (PFDMA) can lead to a portable device that exhibits both high resolution and sensitivity, to meet the needs of today's expanding applications.

The qualitative analysis of the green tea extract using ESI-MS method

The aim of this paper was the identification of the bioactive compounds in the green tea extract enriched with quercetin. The extraction was performed under reflux for 60 min using absolute ethanol at the solid-to-liquid ratio of 1:18 (m/v). The mass spectrometry method with an electrospray interface was applied and tuned with the quercetin standard. Mass spectra were recorded in negative and positive ionization modes with the ion source voltage of 4.95 kV, the source current of 2.61 μA, the capillary temperature of 275 °C, the capillary voltage of 50 V, the sheath gas pressure of 137 KPa and auxiliary gas pressure of 13.9 KPa. In addition to quercetin, the presence of gallic acid, (-)-gallocatechin, 3-O-caffeoylquinic acid, theobromine, 5-O-galloylquinic acid, (+)-catechin, caffeine, epicatechin-3-gallate, (-)-epigallocatechin-3-gallate, 4-p-coumaroylquinic acid, quercetin-3-O-rutinoside, quercetin-3-galactoside, kampferol-3-O-glucoside, apigenin glycoside, theaflavin-3,3'-digallate, thafla­vin-3-gallate and the kaempferol-rhamnose-hexose-rhamnose conjugate was confirmed based on fragmentation patterns available in literature.

Comparative study of laminar and turbulent flow model with different operating parameters for radio frequency-inductively coupled plasma torch working at 3 MHz frequency at atmospheric pressure

This paper provides 2D comparative study of results obtained using laminar and turbulent flow model for RF (radio frequency) Inductively Coupled Plasma (ICP) torch. The study was done for the RF-ICP torch operating at 50 kW DC power and 3 MHz frequency located at BARC. The numerical modeling for this RF-ICP torch is done using ANSYS software with the developed User Defined Function. A comparative study is done between laminar and turbulent flow model to investigate how temperature and flow fields change when using different operating conditions such as (a) swirl and no swirl velocity for sheath gas flow rate, (b) variation in sheath gas flow rate, and (c) variation in plasma gas flow rate. These studies will be useful for different material processing applications.

Microfluidic liquid jet system with compatibility for atmospheric and high-vacuum conditions

We present microfluidic chip based devices that produce liquid jets with micrometer diameters while operating at very low flow rates. The chip production is based on established soft-lithographical techniques employing a three-layer design protocol. This allows the exact, controlled and reproducible design of critical parts such as nozzles and the production of nozzle arrays. The microfluidic chips reproducibly generate liquid jets exiting at perfect right angles with diameters between 20 μm and 2 μm, and under special circumstances, even down to 0.9 μm. Jet diameter, jet length, and the domain of the jetting/dripping instability can be predicted and controlled based on the theory for liquid jets in the plate-orifice configuration described by Gañán-Calvo et al. Additionally, conditions under which the device produces highly reproducible monodisperse droplets at exact and predictable rates can be achieved. The devices operate under atmospheric and under vacuum conditions making them highly relevant for a wide range of applications, for example, for free-electron lasers. Further, the straightforward integration of additional features such as a jet-in-jet is demonstrated. This device design has the potential to integrate more features based on established microfluidic components and may become a standard device for small liquid jet production.

Chemical-Vapor-Assisted Electrospray Ionization for Increasing Analyte Signals in Electrospray Ionization Mass Spectrometry

We report a chemical-vapor-assisted electrospray ionization (ESI) technique to improve the detection sensitivity of ESI mass spectrometry (MS). This simple technique involves introducing a chemical vapor into the sheath gas around the nano-ESI spray tip or through a tubing with its outlet placed close to the spray tip. A variety of chemical vapors were tested and found to have varying degrees of effects on analyte signal intensities. The use of benzyl alcohol vapors in ESI was found to increase signal intensities of standard peptides by up to 4-fold. When this technique was combined with capillary liquid chromatography tandem MS (LC-MS/MS), the number of unique peptides identified in the acid hydrolysate of alpha casein increased by 45% and the number of peptides and proteins identified in a tryptic digest of E. coli cell lysate increased by 13% and 14%, respectively, along with an increased average match score. This technique could also increase the analyte signals for some small molecules, such as phenylephrine, by up to 3-fold. The increased analyte signals observed in the chemical-vapor-assisted ESI process is related to the enhancement of the ionization efficiency in ESI. The method can be readily implemented to an existing ESI mass spectrometer at minimum cost for improving detection sensitivity.

An Initial Study of Aerosol Jet® Printed Interconnections on Extrusion-Based 3D-Printed Substrates

The combination of different additive manufacturing techniques to produce freeform products with multifunctional properties is gaining increasing popularity. In the research presented, Aerosol Jet® Printing (AJP) is combined with extrusion-based 3D printing. AJP starts with an ink to create micro-tracks. These tracks commonly have widths ranging from a few micrometers up to several millimeters and track heights ranging from a few tenths of a micrometer up to several micrometers, unlike extrusion-based 3D printers with which the extruded material usually has a resolution of tenths of millimeters. AJP can therefore be a complementary technique for extrusion-based 3D printing; in this manner, fine high resolution features can be added onto relatively rapidly produced extrusion-based 3D printed parts. Furthermore, AJP can be used to produce electrically conductive tracks to create interconnections, inductors, capacitors, strain gauges, etc. In this paper, the creation of AJP-manufactured interconnects on extrusion-based 3D printed substrates is investigated. The relevant AJP process parameters to take into account are the flow rates of the aerosol, the flow rate of the sheath gas, the temperature settings of the ink and substrate, and the platform speed and nozzle-to-substrate distance. To obtain reliable results, the AJP process parameters are optimized for printing single-layered and multilayered silver ink tracks on extrusion-based 3D-printed surfaces. Important quality output parameters include the dimensions and the electrical properties of the printed interconnects.

Practical and Economical Implementation of Online H/D Exchange in LC-MS

Structural elucidation is an integral part of drug discovery and development. In recent years, due to acceleration of the drug discovery and development process, there is a significant need for highly efficient methodologies for structural elucidation. In this work, we devised and standardized a simple and economical online hydrogen-deuterium exchange methodology, which can be used for structure elucidation purposes. Deuterium oxide (D2O) was infused as a postcolumn addition using the syringe pump at the time of elution of the analyte. The obtained hydrogen/deuterium (H/D) exchange spectrum of the unknown analyte was compared with the nonexchanged spectrum, and the extent of deuterium incorporation was delineated by using an algorithm to deconvolute partial H/D exchange, which confirmed the number of labile hydrogen(s) in the analyte. The procedure was standardized by optimizing flow rates of LC output, D2O infusion, sheath gas, and auxiliary gas using the model compound sulfasalazine. The robustness of the methodology was demonstrated by performing sensitivity analysis of various parameters such as concentrations of analyte, effect of matrices, concentrations of aqueous mobile phase, and types of LC modifiers. The optimized technique was also applied to chemically diverse analytes and tested on various mass spectrometers. Moreover, utility of the technique was demonstrated in the areas of impurity profiling and metabolite identification, taking pravastatin-lactone and N-oxide desloratidine, as examples.

A Label-free Selected Reaction Monitoring Workflow Identifies a Subset of Pregnancy Specific Glycoproteins as Potential Predictive Markers of Early-onset Pre-eclampsia

Pre-eclampsia (PE) is a serious complication of pregnancy with potentially life threatening consequences for both mother and baby. Presently there is no test with the required performance to predict which healthy first-time mothers will go on to develop PE. The high specificity, sensitivity, and multiplexed nature of selected reaction monitoring holds great potential as a tool for the verification and validation of putative candidate biomarkersfor disease states. Realization of this potential involves establishing a high throughput, cost effective, reproducible sample preparation workflow. We have developed a semi-automated HPLC-based sample preparation workflow before a label-free selected reaction monitoring approach. This workflow has been applied to the search for novel predictive biomarkers for PE. To discover novel candidate biomarkers for PE, we used isobaric tagging to identify several potential biomarker proteins in plasma obtained at 15 weeks gestation from nulliparous women who later developed PE compared with pregnant women who remained healthy. Such a study generates a number of "candidate" biomarkers that require further testing in larger patient cohorts. As proof-of-principle, two of these proteins were taken forward for verification in a 100 women (58 PE, 42 controls) using label-free SRM. We obtained reproducible protein quantitation across the 100 samples and demonstrated significant changes in protein levels, even with as little as 20% change in protein concentration. The SRM data correlated with a commercial ELISA, suggesting that this is a robust workflow suitable for rapid, affordable, label-free verification of which candidate biomarkers should be taken forward for thorough investigation. A subset of pregnancy-specific glycoproteins (PSGs) had value as novel predictive markers for PE.

Separation and characterization of nitrated variants of the major birch pollen allergen by CZE‐ESI‐μTOF MS

A CZE-ESI-TOF MS method has been optimized for the separation and identification of nitrated variants of the major birch pollen allergen from Betula verrucosa, isoform 1a (Bet v 1a). In-house nitration of recombinant Bet v 1a was done by peroxynitrite. As a BGE, 10 mmol/L ammonium bicarbonate with pH 7.50 provided best resolution. Nebulizer gas pressure and sheath liquid flow rate of 0.4 bar and 6 μL/min, respectively, maintained CZE selectivity and constituted stable electrospray conditions. A sheath liquid composition of 75% v/v methanol with 0.1% v/v formic acid in ultrapure water resulted in highest signal intensities. Alternatively, methanol could be replaced by 50% v/v isopropanol. Two modified allergen products derived from reaction mixtures that contained different amounts of the nitration reagent were compared by the elaborated CZE-ESI-TOF MS method. Up to twelve different Bet v 1a variants with one- to sixfold nitration could be distinguished. Several allergen fractions of equivalent nitration grade were resolved. Their different migration times indicate site-specific nitration with concomitant differences in pI and maybe also in hydrodynamic radius. The method allows for a characterization of in-house nitrated allergen samples that are intended for testing the postulated enhanced allergenicity of nitrated Bet v 1a variants.

Stepwise optimization approach for improving LC‐MS/MS analysis of zwitterionic antiepileptic drugs with implementation of experimental design

In this article, a step-by-step optimization procedure for improving analyte response with implementation of experimental design is described. Zwitterionic antiepileptics, namely vigabatrin, pregabalin and gabapentin, were chosen as model compounds to undergo chloroformate-mediated derivatization followed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis. Application of a planned stepwise optimization procedure allowed responses of analytes, expressed as areas and signal-to-noise ratios, to be improved, enabling achievement of lower limit of detection values. Results from the current study demonstrate that optimization of parameters such as scan time, geometry of ion source, sheath and auxiliary gas pressure, capillary temperature, collision pressure and mobile phase composition can have a positive impact on sensitivity of LC-MS/MS methods. Optimization of LC and MS parameters led to a total increment of 53.9%, 83.3% and 95.7% in areas of derivatized vigabatrin, pregabalin and gabapentin, respectively, while for signal-to-noise values, an improvement of 140.0%, 93.6% and 124.0% was achieved, compared to autotune settings. After defining the final optimal conditions, a time-segmented method was validated for the determination of mentioned drugs in plasma. The method proved to be accurate and precise with excellent linearity for the tested concentration range (40.0 ng ml(-1)-10.0 × 10(3) ng ml(-1)).

High Sensitive Elemental Analysis of Single Yeast Cells (Saccharomyces cerevisiae) by Time-Resolved Inductively-Coupled Plasma Mass Spectrometry Using a High Efficiency Cell Introduction System

Trace elemental analysis of single yeast cells with time-resolved inductively coupled plasma mass spectrometry (ICP-MS) was successfully carried out, where a high efficiency cell introduction system (HECIS) consisting of the high performance concentric nebulizer (HPCN) and a low-volume (15 mL) on-axis spray chamber utilizing a sheath gas flow were used. Cell adsorption to the flow injector and sample tubing was reduced with the addition of a simple 4.3 mmol L(-1) of NaCl solution to the cell suspension and cell flowing liquid, allowing consecutive measurements without fear of significant contamination from previous measurements. Initially using a quadrupole mass analyzer ICP-MS (ICP-QMS) at its lowest integration time (10 ms), current spikes corresponding to separate cell events were detected for several elements (Mg, P, Ca, Mn, Fe, Cu, and Zn) on the introduction of the cell suspension. On comparing the number of peaks in the spectrum for phosphorous with the cell count using a haemocytometer, a reproducible cell transport efficiency of 75.0 ± 4.7% was achieved. Preliminary experiments into using time of flight ICP-MS (ICP-TOFMS) for single-cell analysis were carried out, allowing quasi-simultaneous multielement detection. The spectra of Mg, P, Ca, Mn, Fe, Cu, and Zn, with a time resolution of 1 ms were simultaneously obtained in one measurement. A relatively strong correlation was observed for the spectra between P and Zn (correlation factor 0.69), P and Mg (0.63), and Mg and Zn (0.63). These results indicate that the time resolved quasi-simultaneous multielement measurement may be useful for the correlation analysis of multielements in cells.

Optimization of Aerosol Jet Printing for High-Resolution, High-Aspect Ratio Silver Lines

Aerosol jet printing requires control of a number of process parameters, including the flow rate of the carrier gas that transports the aerosol mist to the substrate, the flow rate of the sheath gas that collimates the aerosol into a narrow beam, and the speed of the stage that transports the substrate beneath the beam. In this paper, the influence of process parameters on the geometry of aerosol-jet-printed silver lines is studied with the aim of creating high-resolution conductive lines of high current carrying capacity. A systematic study of process conditions revealed a key parameter: the ratio of the sheath gas flow rate to the carrier gas flow rate, defined here as the focusing ratio. Line width decreases with increasing the focusing ratio and stage speed. Simultaneously, the thickness increases with increasing the focusing ratio but decreases with increasing stage speed. Geometry control also influences the resistance per unit length and single pass printing of low-resistance silver lines is demonstrated. The results are used to develop an operability window and locate the regime for printing tall and narrow silver lines in a single pass. Under optimum conditions, lines as narrow as 20 μm with aspect ratios (thickness/width) greater than 0.1 are obtained.

Process control for the synthesis of ZrO2 nanoparticles using FSP at high production rate

A numerical method of combining CFD with the particle dynamics was developed to study the effect of processing parameters on the formation of nanoparticles by Flame Spray Pyrolysis for up scaling the synthesis of zirconia nanoparticles. This investigation employed a commercial CFD code to simulate the gas flow field and droplet dynamics while three numerical models were developed to predict dynamic viscosity and surface tension of precursor solutions, the sauter mean diameter (SMD) of droplets during atomization and the particle growth inside the flame by coagulation and sintering. The simulation results were compared with experimental data available in this study and literature. The validated models were used to predict the effect of processing parameters, in particular, the effect of pressure drop, sheath gas, oxidant/mixture volume feed ratio (VFR), production rate and precursor concentration on flame dynamics and particle growth. The results show that increasing pressure drop and VFR will be able to decrease the residence time and sintering of nanoparticles in the flame. The variation of inlet sheath gas feeding had a negligible effect on the fluid flow and final particle size. The results also showed that by keeping the VFR and pressure drop at a fixed predicted value, similar particle size can be achieved at higher production rates using fixed precursor concentration.