Inlet End Research Articles

Measurement of external ion injection and trapping efficiency in the ion trap mass spectrometer and comparison with a predictive model

The efficiency of injecting and trapping ions from an external ion source in a quadrupole ion trap mass spectrometer was measured and compared against a simulation employing a simple hard-sphere collision model. A commercial ion trap mass spectrometer was modified with the addition of a variable energy ion gun, split Faraday cup/electron multiplier detector, and the capability to measure the ion current incident on the ion trap inlet and exit end caps. The entire instrument was modeled using the ion optics simulation program SIMION and user programs were applied in SIMION which modeled the collisions between the injected ions and the helium buffer gas. The model was based on simple hard-sphere collision physics with randomized collision angles and collision probability converging to the mean free path (mfp); the helium buffer gas was assumed to be at rest relative to the injected ions. The measured trapping efficiency of Cs + with helium buffer gas at optimum conditions was 3–5%. The trapping efficiency predicted by the model and the dependence on buffer gas pressure (mfp) agreed with the measured efficiencies within the uncertainties of the model predictions and experimental variance. The fidelity of the simulation was shown to be sensitive to the spatial resolution of the model when predicting the dependence of trapping efficiency on q z. It was concluded that a hard-sphere collision model was adequate for predicting the effects of helium buffer gas pressure on ion injection and trapping within the range of injection energies and buffer gas pressures tested.

Sol-gel capillary microextraction.

Sol-gel capillary microextraction (sol-gel CME) is introduced as a viable solventless extraction technique for the preconcentration of trace analytes. To our knowledge, this is the first report on the use of sol-gel-coated capillaries in analytical microextraction. Sol-gel-coated capillaries were employed for the extraction and preconcentration of a wide variety of polar and nonpolar analytes. Two different types of sol-gel coatings were used for extraction: sol-gel poly(dimethylsiloxane) (PDMS) and sol-gel poly(ethylene glycol) (PEG). An in-house-assembled gravity-fed sample dispensing unit was used to perform the extraction. The analysis of the extracted analytes was performed by gas chromatography (GC). The extracted analytes were transferred to the GC column via thermal desorption. For this, the capillary with the extracted analytes was connected to the inlet end of the GC column using a two-way press-fit fused-silica connector housed inside the GC injection port. Desorption of the analytes from the extraction capillary was performed by rapid temperature programming (at 100 degrees C/min) of the GC injection port. The desorbed analytes were transported down the system by the helium flow and further focused at the inlet end of the GC column maintained at 30 degrees C. Sol-gel PDMS capillaries were used for the extraction of nonpolar and moderately polar compounds (polycyclic aromatic hydrocarbons, aldehydes, ketones), while sol-gel PEG capillaries were used for the extraction of polar compounds (alcohols, phenols, amines). The technique is characterized by excellent reproducibility. For both polar and nonpolar analytes, the run-to-run and capillary-to-capillary RSD values for GC peak areas remained under 6% and 4%, respectively. The technique also demonstrated excellent extraction sensitivity. Parts per quadrillion level detection limits were achieved by coupling sol-gel CME with GC-FID. The use of thicker sol-gel coatings and longer capillary segments of larger diameter (or capillaries with sol-gel monolithic beds) should lead to further enhancement of the extraction sensitivity.

Optimization and evaluation of low-pressure gas chromatography–mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity

A fast method of analysis for 20 representative pesticides was developed using low-pressure gas chromatography–mass spectrometry (LP-GC–MS). No special techniques for injection or detection with a common quadrupole GC–MS instrument were required to use this approach. The LP-GC–MS approach used an analytical column of 10 m×0.53 mm I.D., 1 μm film thickness coupled with a 3 m×0.15 mm I.D. restriction capillary at the inlet end. Thus, the conditions at the injector were similar to conventional GC methods, but sub-atmospheric pressure conditions occurred throughout the analytical column (MS provided the vacuum source). Optimal LP-GC–MS conditions were determined which achieved the fastest separation with the highest signal/noise ratio in MS detection (selected ion monitoring mode). Due to faster flow-rate, thicker film, and low pressure in the analytical column, this distinctive approach provided several benefits in the analysis of the representative pesticides versus a conventional GC–MS method, which included: (i) threefold gain in the speed of chromatographic analysis; (ii) substantially increased injection volume capacity in toluene; (iii) heightened peaks with 2 s peak widths for normal MS operation; (iv) reduced thermal degradation of thermally labile analytes, such as carbamates; and (v) due to larger sample loadability lower detection limits for compounds not limited by matrix interferences. The optimized LP-GC–MS conditions were evaluated in ruggedness testing experiments involving repetitive analyses of the 20 diverse pesticides fortified in a representative food extract (carrot), and the results were compared with the conventional GC–MS approach. The matrix interferences for the quantitation ions were worse for a few pesticides (acephate, methiocarb, dimethoate, and thiabendazole) in LP-GC–MS, but similar or better results were achieved for the 16 other analytes, and sample throughput was more than doubled with the approach.

SIMULATING EMITTER CLOGGING IN A MICROIRRIGATION SUBUNIT

A mathematical model was developed to simulate the effects of emitter clogging on subunit hydraulics. The modelconsists of a set of equations based on fundamental hydraulic principles and inlet lateral discharge relationships, and usesa nonlinear equation solver. The model was used to simulate different clogging rates (0% to 100%) and different clogginglocations within the subunit. Pressure head was monitored at the pump, manifold inlet, manifold midpoint, and manifolddownstream end. The results of the study indicate that to reasonably detect clogging rate and location, the pump pressure headvalue and manifold pressure head profile need to be monitored. Pressure transducers are therefore needed at the pump,manifold inlet point, and manifold endpoint. Model results were verified by using experimental data collected in a previousstudy. The RMSE was found to be 0.13 kPa between model results and experimental data at the upstream point of the manifold,and 1.11 kPa at the downstream end of the manifold. Clogging was found to decrease inlet lateral discharge for cloggedlaterals and increase the lateral inlet discharge for unclogged laterals. In addition, pump response to clogging was found tobecome progressively smaller as the clogging location moved further from the pump.

Trapped acoustic modes in aeroengine intakes with swirling flow

A theoretical model of an aeroengine intake–fan system is developed in order to show the existence of acoustic resonance in the intake. In general this phenomenon can be linked to instabilities in aircraft engine inlets.The model incorporates a slowly varying duct intake and accounts for the swirling flow downstream of the fan. The slow axial variation in cross-section gives rise to turning points where upstream-propagating acoustic modes are totally reflected into downstream-propagating modes. The effect of the swirling flow downstream can be to cut off a mode which is cut on upstream of the fan. It is shown that these two aspects of the flow, coupled with the effects of the fan (represented by an actuator disc), can lead to acoustic modes becoming trapped in the intake, thus giving rise to pure acoustic resonance.A whole range of system parameters, such as axial, fan and swirl Mach numbers, which satisfy the conditions for resonance are identified. The effects of a stationary blade row behind the fan are also considered leading to a second family of resonant states. In addition we find resonance due to reflection of acoustic modes at the open (inlet) end of the duct.

Reconditioning of Gas Turbine Components by Heat Treatment

At the high operating temperatures experienced within a gas turbine, creep damage is a major life-limiting factor. This is especially true for components which are highly stressed and closest to the hot gas inlet end of the machine, such as the rotating blades in this area. The ability to recover the creep properties of used gas turbine components might enable their service lives to be increased considerably. Thereby, maintenance costs could be reduced. Previous research into the feasibility of reconditioning crept superalloys by heat treatment will be reviewed and perceived limitations identified. The current work will add to knowledge on the effects of conventional recovery techniques and will explore potential new heat treatment regimes. The experimental and analytical methods to be used will be both described and supported by preliminary results.

Interrelationships between biological, chemical, and physical processes as an analog to clogging in aquifer storage and recovery (ASR) wells

Laboratory columns were used to understand and predict bore clogging issues at a South Australian recycled water aquifer storage and recovery site, before field trials proceeded. The columns were used to study biogeochemical processes resulting from the continuous injection of recycled water into an aquifer matrix. The results showed that despite levels of suspended solids (SS) between 3–4 mg/l in the influent, flow rates (hydraulic conductivities) were maintained at 20–50% of initial flow through three identical columns for a period of 22 days. An initial decline in the hydraulic conductivity ( K) through the columns was evident early in the experiment, and decreased from 0.78 m/day to 0.062 m/day in the first 7 days of the experiment. This was thought to be due to physical clogging by suspended solids and then biological clogging by biomass accumulation and polysaccharide production at the inflow end of the columns. The physical bioclogging was relieved midway through the experiment due to calcite dissolution mainly at the inlet end of the columns. Calcite reprecipitation at the outflow end of the columns was evident from SEM micrographs.

Capillary electrochromatography of 1-phenyl-3-methyl-5-pyrazolone derivatives of some mono-and disaccharides

A packing procedure was adopted for capillary electrochromatography (CEC) that produces capillary columns with high separation efficiencies. The columns were fully packed, 50 cm long, with UV detection being performed through the packed section 30 cm from the inlet end. The CEC experiments were run at ambient pressure, with no additional pressure applied to the ends of the column. The stationary phase (octadecyl silica (ODS), 5 μm) promoted a high velocity electroosmotic flow (EOF), enabling rapid and efficient separation of a hydrocarbon test mixture. Some 1-phenyl-3-methyl-5-pyrazolone (PMP) derivatives of mono- and disaccharides were baseline separated, using a 5 mM NaH2PO4 in 80% acetonitrile and 20% water (v/v) buffer solution. CEC shows promise for future applications in carbohydrate analysis.

Assay for the determination of low dosage form of formoterol dry syrup by capillary electrophoresis with head-column field-amplified sample stacking

The development of a capillary zone electrophoresis method with head-column field-amplified sample stacking injection for the determination of formoterol (FMTR) in a low dosage dry syrup form was described. To obtain the highest sensitivity, the sample solution was prepared by high content of organic solvent with the presence of a small amount of H + (60–100 μM) and the capillary inlet end was dipped in water before electroinjection. This method was fully validated in terms of repeatability (RSDs for migration time, peak area of FMTR and peak area ratio between FMTR and I.S. at 1 μg/ml of FMTR was 0.76, 1.10 and 0.55% respectively), reproducibility (RSDs from different capillaries, analytes, days and instruments were 1.52%, 1.04%, 1.16% and 1.93% respectively), linearity ( y=0.827 x−0.085, r=0.9993 ( n=6) over the range of 0.25–2.0 μg/ml), limits of quantitation, ruggedness and robustness. The method was applied to the determination of the drug in commercial dry syrup preparation (recovery was 100.9%, RSD=1.5%, n=5) and proved to be fast and reliable for the quantitation analysis of FMTR in the pharmaceutical form.

Combination of flow injection with capillary electrophoresis. Part 6.: A bias-free sample introduction system based on electroosmotic-flow traction

A bias-free sample injection method based on electroosmotic-flow (EOF) traction was developed for the combined flow injection-capillary electrophoresis system. A Nafion joint implemented at a capillary fracture close to the capillary inlet was used for isolating the electric field during the split-flow sample injection, the sample solution being drawn into the capillary by EOF without bias effects. An electronic time relay system was adopted to control the switching of high voltage between the capillary inlet end and the joint. The peak area ratios of two model compounds, dimethyl sulfoxide and benzoic acid obtained using the proposed system were identical to those with gravity injection. Relative standard deviations of 0.5–2.5% ( n = 32) were achieved for peak height and peak area evaluation in the consecutive injections of a series of replicate sample solutions at a sampling frequency of 15 h −1 . Similar performance of the system was obtained with a reversed EOF background electrolyte after reversing the electrode polarity for a mixture of the anions, Cl −, SO 4 2−, NO 3 − and F − using indirect UV detection. The performance of the system for the analysis of real samples was demonstrated by bias-free sample injection in the separation of caffeine, theobromine and theophylline in beverage samples with satisfactory recoveries in the 92–107% range.

Pressure wave propagation by gas expansion in a high vacuum tube

In this article we describe an unsteady tube flow model which accounts for the effect of contracted flow around the entrance orifice of the tube which was developed with the aim of preventing vacuum hazards at scientific experimental facilities. Setting an atmospheric pressure drop between the outside and inside of the vacuum tube makes the model applicable to high vacuum, although the model is based on continuous fluid dynamics. We installed an orifice on the inlet end of the tube in the model, and investigated the orifice aperture effect on the propagation velocity of pressure waves.

Ozone-induced respiratory illness during the repair of a portland cement kiln.

Workers at a portland cement plant had experienced acute respiratory and eye irritation when performing maintenance inside a kiln. These episodes were associated with a bleach-like odor, which was only reported during maintenance operations. An industrial hygiene investigation was conducted to determine the cause of the illness. While workers replaced refractory brick inside the kiln, air samples were collected for chlorine, sulfur dioxide, inorganic acid, ozone, and dust. After the rebricking was completed and all the workers had exited the kiln, its electrostatic precipitator was reduced to half power and the induced-draft (ID) fan was turned off to recreate conditions present during illness episodes. Chlorine, inorganic acid, and ozone were not detected, and only trace concentrations of sulfur dioxide were detected while workers were inside the kiln. However, when conditions present during previous episodes were recreated, the bleach-like odor was soon evident. Chlorine was not detected, but 0.09 to 0.11 ppm of ozone was measured at the discharge end of the kiln, and 4.5 ppm was measured at the inlet end. Within a half hour after the electrostatic precipitator was turned off and the ID fan was turned on, the ozone concentrations decreased to background levels of 0.02-0.03 ppm. Somewhat lower ozone exposures may have occurred during previous kiln maintenance operations due to more open access portals, but previous episodes of eye and respiratory irritation were probably caused when ozone, generated by the electrostatic precipitator, back-drafted into the kiln after the ID fan was turned off.

The magnetic field and performance calculations for an electromagnetic pump of a liquid metal

For an annular-type electromagnetic pump of a liquid metal, the magnetic field is found in closed form by means of the Fourier transform method for two-dimensional field analysis based on an equivalent current sheet model, so that the terms contributing to the normal thrust and the end effect are analytically identified. Analytical solutions for the magnetic vector potentials are compared with numerical ones obtained from the finite difference equation, and they turn out to be in good agreement regardless of the assumption of infinite permeability used in the analytical approach. As a result of closed-form solutions, the electromagnetic body force exerted on a liquid metal flow and the efficiency of the pump are calculated without going through tedious time-consuming numerical work usually accompanied by troublesome convergence problems. The calculated results for estimating the influence of end effects on the performance of the electromagnetic pump clearly show that the end effects give rise to the obstructive force to the liquid metal flow at inlet and outlet ends of the pump. In addition, the efficiency is found to be lowered due to end effects, especially when the speed of the flow is high.

Waterborne parasite filter

In GB2315427 Edward A Gardyne and Edward D Garoyne describe a filter for removing waterborne parasites. It uses a sintered stainless steel filter member preferably of 1 to 3 micrometre pore size. The filter is a cylinder of sintered material having a male thread at one end and a blanc disc at the other which is screwed into the inlet end of a two part threaded housing. The other part has an outlet and a domed end. The housing can be of stainless steel or plastic such as uPVC. The filter can be removed for cleaning or cleaned by an internal brush rotated by an external electric motor and/or backwashed either periodically or automatically.

Stepper Motor Controlled Micro Gas Valve Inlet System for Gas Chromatography

A novel gas valve inlet system for gas chromatography is described. The device incorporates a capillary sample gas delivery tube containing a small orifice in its side from which sample vapor continuously flows. A precision micro stepper motor is used to translate the sample delivery tube parallel to its axis so that the orifice passes by the end of the fused silica separation column. The inlet end of the column and the sample delivery tube are housed in a pressurized injection port which also contains purge flows to vent sample between injections. Two operating modes are described. In the sweep mode, the orifice sweeps past the column end at a constant, adjustable velocity. In the park mode, the orifice is parked in front of the column end for a software selectable time. Injection sample size and bandwidth are adjustable. Bandwidths (σ) as small as a few milliseconds make the inlet suitable for high-speed gas chromatography as well as conventional GC.

An On-Line Electrophoretic Concentration Method for Capillary Electrophoresis of Proteins

A simple on-line electrophoretic concentration method for capillary electrophoresis of proteins with a semipermeable hollow fiber is proposed. A short, semipermeable hollow fiber is connected to the inlet end of a capillary. An injection electric field is applied across the hollow fiber. Protein samples are electromigrated into the hollow fiber from a sample vial. Since the protein ions cannot pass through wall of the hollow fiber, protein ions are concentrated in the hollow fiber. After a certain period of injection (concentration) time, an electric field is applied across the hollow fiber and the capillary, and a conventional CE is carried out. The concentration effect of the method has been demonstrated successfully with model protein samples, cytochrome c, lysozyme, ribonuclease A, and α-chymotrypsinogen A. Experimental results show that the concentration factor is increased with the injection (concentration) time and the electrophoretic mobility of the proteins. When the injection (concentration) time is 60 s, CE detection limits of the model proteins can be lowered by 1000-fold for the present method. Factors affecting the concentration factors and the further improvements of the method are discussed.

Reformer for fuel cell system

A number of embodiments of reformers for reforming fuel for a fuel cell that includes an elongated catalyst bed with fuel to be reformed being delivered at one end of the bed and extracted from the other end of the bed. Heat is applied to a greater extent at the inlet end of the catalyst bed than the outlet end to prevent the formation of carbon monoxide in the products delivered from the outlet. In all embodiments, the catalyst bed has a spiral configuration and the fuel is heated before it is delivered to the catalyst bed. In some embodiments the same heat sources are employed for heating both the fuel and the catalyst bed.

Solid phase microextraction coupled to capillary electrophoresis

An on-column interface, coupling the solid phase microextraction (SPME) sampling technique with capillary electrophoresis (CE), has been constructed. This interface facilitates the direct insertion of a thin silica fiber into the inlet end of a separation capillary and, therefore, the zero-dead volume connection requirement for hyphenation between SPME and CE is fully realized. The performance of the interface was evaluated by SPME–CE analysis of the priority pollutant phenols using a laboratory-made 40 µm od poly(acrylate) (PA)-coated silica fiber connected to a 75 µm id separation capillary. The results clearly demonstrate that the interface is effective for on-line coupling SPME with CE.

Heat transfer in a through-ventilated induction motor

The effects of varying the cooling air flow and its distribution on the heat transfer in a high-voltage, strip-wound, four-pole induction motor are reported. The flow variations were achieved by altering the motor speed, by removing the wafters, by increasing the flow resistance of the motor air inlets, or by insertion of heat transfer augmentation devices in the stator-frame ducts. Heat transfer coefficients were deduced from the measurement of input power, and from miniature heat flux gauges attached to the surfaces. The overall heat transfer coefficient on the end-winding at the air outlet end (the fan end) was roughly double that at the air inlet end, the converse of the situation for lap and concentric wound motors. Large spatial variations in the end-winding local heat transfer coefficients occurred. This is attributed to the open nature of the winding which results in the individual loops behaving as separate bodies, each with a flow pattern dependent upon the angle of the approaching flow. There was a large increase in the overall heat transfer coefficient on the winding at the fan end when the wafters were removed. The use of transverse ribs in the stator-frame ducts was found to enhance heat transfer.

Stability and Emissions of Lean, Turbulent, Premixed Flames with Very Lean Coflow

The potential for improving lean stability and reducing NO x emissions of combustion systems by employing an ultralean, partially premixed fuel injection strategy was examined experimentally. The test cone guration was a coannular combustor cone guration at atmospheric pressure with a simulated natural gas fuel. The core e ow consisted of fuel premixed with air; the coe ow was either fuel premixed with air, sufe ciently lean to be below the e ammability limit, or air only. The e ame was stabilized on axisymmetric, bluff body e ameholders sting-mounted along the centerline of the combustor. Mounting the e ameholder from the inlet end of the combustor resulted in a more stable e ame under lean conditions than was the case for the e ameholder mounted from above the combustor exit. When either e ameholder was located sufe ciently far downstream from the core e ow nozzle tip, an enhancement of lean stability was achieved by increasing the fuel content of the coe ow stream. This change in stability can be accounted for by dee ning an effective equivalence ratio at the e ameholder location that takes into account the presence of coe ow fuel and the core/coe ow mixing. The addition of fuel to the coe ow resulted in up to a factor of 4 lower levels of total NO x compared with the case with fuel in the core e ow only. This decrease in NOx was accompanied by a drop in peak temperature. The total exhaust NO x concentration was comparable for all cone gurations when run close to their corresponding lean limits. These results suggest that changing the distribution of injected fuel can have a benee cial impact on the lean-limit stability and emissions characteristics of turbulent, premixed combustion systems.