Alternate Gas Research Articles

Determination of chromium, manganese and vanadium in sediments and soils by modifier—free slurry sampling electrothermal atomic absorption spectrometry

Slurried sediment and soil samples of the certified reference materials with a highly elevated level of the metals of interest (Mn, Cr and V) were analysed by electrothermal atomic absorption spectrometry (ETAAS) with Zeeman effect background correction. The method of slurry preparation and time-temperature programmes were optimized and, finally, the use of chemical modifiers was not necessary. The effect of alternate spectral lines and gas mini-flows on characteristic masses of analytes was studied. The homogeneity of samples and the influence of short sample grinding were also discussed. The simple, aqueous standard based calibration graphs (except Mn at the concentration > 1000 mg kg−1) were applied for the quantification of results. The results of determinations obtained by slurry sampling agreed well with the cetified values, and the relative standard deviations (RSDs) for the over-all analytical procedure repeatability (at slurries concentration level about 2 mg/2 ml) were less than 9.5%, except manganese (10.4%).

A comparison of the hemodynamic and ventilatory effects of abdominal insufflation with helium and carbon dioxide in young swine

Abdominal CO 2 insufflation has been shown to cause hypercarbia, acidemia, and decreased oxygenation in a pediatric animal model. Such metabolic derangements have prompted a search for alternative insufflation gases. This study compares the hemodynamic and ventilatory changes that occur during pneumoperitoneum with CO 2 and helium. Four juvenile swine were intubated and given general anesthesia. Minute ventilation was adjusted to obtain a baseline P co 2 of between 32 and 36 mm Hg, and was kept constant for the duration of the experiment. The subjects initially were insufflated with CO 2 or helium at a pressure of 10 mm Hg. Peak ventilatory pressure, end-tidal CO 2 (ETCO 2) arterial pH, P co 2, P o 2, and right atrial and inferior vena caval pressures were measured before and during a 1-hour insufflation period. After desufflation, P co 2 and pH were restabilized. The same parameters were then measured during reinsufflation with the alternate gas. CO 2 insufflation caused significant decreases in pH, from 7.51 ± 0.03 to 7.32 ± 0.06, and P o 2 increased from 261 ± 49 to 189 ± 33 mm Hg. P co 2 increased from 35.0 ± 1.4 to 57.9 ± 6.3 mm Hg. ETCO 2 also increased, from 29.0 ± 2.2 to 47.2 ± 5.0 mm Hg. Helium insufflation caused pH to decrease from 7.51 ± 0.01 to 7.42 ± 0.04. P co 2 increased from 32.8 ± 0.8 to 43.5 ± 3.9 mm Hg, and ETCO 2 increased from 27.8 ± 0.5 to 36.8 ± 3.1 mm Hg. These alterations were significantly less than those with CO 2 pneumoperitoneum. P o 2 decreased as well—from 266 ± 30 to 212 ± 21 mm Hg. During insufflation with both gases, peak ventilatory pressure and right atrial pressure increased slightly, and inferior vena caval pressure increased significantly. Abdominal insufflation with CO 2 or helium causes hypercarbia, acidemia, and increased ETCO 2 in this juvenile animal model. These derangements are significantly less with helium. This gas may prove to be the more suitable insufflation agent for pediatric patients.

Prospective comparison of helium versus carbon dioxide pneumoperitoneum

Background: During prolonged laparoscopic operations with carbon dioxide (CO2) pneumoperitoneum (PP), hypercapnia with significant acidosis has been reported to occur in some patients with pulmonary dysfunction. An alternate inert insufflation gas like helium (He) could avoid this problem. Methods: This prospective, IRB-approved study compared the cardiopulmonary response in 20 patients with both CO2 and He PP. With the minute ventilation held constant, baseline arterial blood gases and ventilatory and cardiac parameters were obtained after anesthetic induction but prior to CO2 PP. All values were repeated at 20 to 30 and 40 to 60-minute intervals after the insufflation of CO2 PP, then again during He PP. Values were compared by a paired t test analysis. Results: Patients experienced significant hypercapnia during CO2 PP when compared with baseline arterial blood gases, but all values returned to baseline levels during He PP. Conclusions: He PP is an effective alternative to CO2 PP for a laparoscopic cholecystectomy avoiding CO2 retention and subsequent acidosis. Carbon dioxide retention may be dangerous in patients with pulmonary dysfunction who undergo laparoscopy. (Gastrointest Endosc (1996;43:38-41.)

Prospective comparison of helium versus carbon dioxide pneumoperitoneum

Background: During prolonged laparoscopic operations with carbon dioxide (CO2) pneumoperitoneum (PP), hypercapnia with significant acidosis has been reported to occur in some patients with pulmonary dysfunction. An alternate inert insufflation gas like helium (He) could avoid this problem. Methods: This prospective, IRB-approved study compared the cardiopulmonary response in 20 patients with both CO2 and He PP. With the minute ventilation held constant, baseline arterial blood gases and ventilatory and cardiac parameters were obtained after anesthetic induction but prior to CO2 PP. All values were repeated at 20 to 30 and 40 to 60-minute intervals after the insufflation of CO2 PP, then again during He PP. Values were compared by a paired t test analysis. Results: Patients experienced significant hypercapnia during CO2 PP when compared with baseline arterial blood gases, but all values returned to baseline levels during He PP. Conclusions: He PP is an effective alternative to CO2 PP for a laparoscopic cholecystectomy avoiding CO2 retention and subsequent acidosis. Carbon dioxide retention may be dangerous in patients with pulmonary dysfunction who undergo laparoscopy. (Gastrointest Endosc (1996;43:38-41.)

Synthesis of NH 3 on Fe, Sm and Sm 2Fe 17 surfaces

Fe, Sm and Sm 2Fe 17 films with amorphous-like structures were prepared under ultrahigh vacuum conditions. These metal surfaces were alternately exposed to H 2 or N 2 gas to measure the reactivities of the gases with the metals at 298 K. During the alternate gas exposures, NH 3 synthesis on the metal surfaces was examined by measuring the partial pressures in the system. NH 3 synthesis was detected during the H 2 exposure of an Fe surface with H 2 and N 2 pre-adsorption layers; during the N 2 exposure of an Sm hydride (SmH 2+ x ) surface; during the H 2 exposure of an Sm hydride (SmH 2+ x ) surface with N 2 pre-adsorption layers; and during the N 2 exposure of a surface of a hydrogen solution phase of Sm 2Fe 17(Sm 2Fe 17H 0.6). During the N 2 exposure of Sm 2Fe 17H 0.6, rapid H 2 desorption from the sample was observed, indicating that the N atoms expel H atoms from the Sm 2Fe 17H 0.6. Highly catalytic features of these modified metal surfaces are reported.

Enhanced selectivity in ion mobility spectrometry analysis of complex mixtures by alternate reagent gas chemistry

Ion mobility spectrometry (IMS) analysis of a complex mixture of volatile organic compounds (VOCs) and organophosphorus compounds (OPCs) at vapor levels of 10–40 mg/m 3 produced mobility spectra with broad profiles illustrating limitations of ion mobility spectrometry (IMS) for screening such mixtures. Preseparation of this mixture with a gas Chromatograph inlet to an ion mobility spectrometer enhanced analytical selectivity although OPC detection was complicated by co-elution with other VOCs. Water reagent gas in the ion source of the ion mobility spectrometer yielded 46 gas Chromatographic peaks in a mixture of 45 VOCs and 19 OPCs. Co-elution of two materials was observed in eight of the Chromatographic peaks and co-elution of three materials occurred in four instances. Further selectivity was gained using reagent gases of elevated proton affinity in the ion source. Reagent gas chemistry for acetone and dimethylsulfoxide reduced the number of GC peaks to 26 and 20, respectively. Moreover, spectral integrity and quantitative response for OPCs were retained at 50 to 1000 pg levels with these reagent gases. For OPCs, analyte ions were shown to be of the type M 2H + under these conditions of analysis and the mobilities of the product ions were independent of reagent gas. Reduced mobility values were assigned to OPC spectra using a well-characterized OPC ion as the reference. Spectral profiles and reduced mobilities suggested that the OPC product ions were not clustered with reagent gas molecules at 100 °C.

The effect of NH 3 and/or SO 2 on the compositional and histological characteristics of sorghum stover

Two experiments were conducted to determine the effects of chemical treatments on the compositional and histological characteristics of sorghum stover. In Experiment 1, chopped sorghum stover was placed inside plastic bags, where 5% of either NH 3 applied as ammonium hydroxide or SO 2 applied as gas, was injected. After 21 days in contact with the respective gas, bags were opened, aerated for 7 days and prepared for chemical analysis and microscopical observations. Compared with an untreated control, treatment with NH 3 increased total nitrogen, non-protein nitrogen, protein nitrogen, acid detergent fiber nitrogen, and in vitro dry matter disappearance and decreased the acid detergent fiber (ADF) contents of stover; SO 2-treated stover had a lower ADF content. In Experiment 2, each chemical was applied to stover previously treated with the alternate gas. In general, the compositional effects followed the same trend as in the previous experiment, although they seemed to be more severe. Scanning electron microscopy showed the extent of the stover tissue damage inflicted by the chemical additives applied.

Theory of Viscous Fingering in Two Phase, Three Component Flow

ABSTRACT When a mobile fluid, such as gas, displaces less mobile fluids, such as oil and water, a viscous instability develops and the injected fluid fingers through the system leading to early breakthrough and poor recovery. In a WAG process (Water Alternate Gas) water and a miscible solvent (gas) are injected into a reservoir containing water and oil. Compared with a miscible flood, when only solvent is injected, fingering can be suppressed by the simultaneous injection of water, if it reduces the apparent mobility contrast between the injected and displaced fluids. In order to understand and control this instability, it is necessary to be able to predict the expected extent of fingering. The behavior of a miscible flood, with only hydrocarbon flowing, can be modeled successfully using a Todd & Longstaff fractional flow. We modify the Todd and Longstaff model self-consistently to account for fingering in multi-component systems. The method is verified for WAG floods. The empirical flow equations are solved analytically in one dimension and the results are in excellent agreement with the averaged saturation and concentration profiles computed using two dimensional high resolution simulation, for a variety of injected water saturations, in both secondary and tertiary displacements.

Effect of photo-irradiation on the growth of ZnSe in metalorganic molecular beam epitaxy

The photo-irradiation effect on the growth of ZnSe in metalorganic molecular beam epitaxy (MOMBE) using dimethylzinc (DMZn) and dimethylselenide (DMSe) as source gases has been investigated. It was revealed that a Se-stabilized (2×1) reconstruction changed to Zn-stabilized c(2×2) by irradiating a high-pressure Hg lamp to the surface under simultaneous supply of MO gases. In the case of growth under alternate gas supply mode, the I d 1 emission, which originates from an exciton bound to deep acceptor, was much reduced in intensity if the lamp was irradiated during the DMZn gas supply, while the Y emission, which is reported to originate from an exciton bound to a structural defect, newly appeared by the irradiation during the DMSe gas supply. It was found that photo-irradiation not only enhances desorption of Se atoms from the surface during the DMSe supply, but is also effective for the perfection of Zn-stabilized surface during the DMZn supply.

How to predict viscous fingering in three component flow

In a WAG process (Water Alternate Gas), water and a miscible solvent (gas) are injected into a reservoir containing water and oil. The solvent will finger through the oil, leading to early breakthrough and poor recovery. Compared with a miscible flood, when only solvent is injected, fingering is supressed by the simultaneous injection of water, since this reduces the apparent mobility contrast between the injected and displaced fluids. The fingering in a miscible flood, with only hydrocarbon flowing, can be modelled successfully using a Todd and Longstaff fractional flow. In this paper, we demonstrate how to modify the effective Todd and Longstaff mobility ratio self-consistently to account for fingering in three component systems. The resultant empirical equations of flow are solved exactly in one dimension and are in excellent agreement with the averaged saturation and concentration profiles computed using two dimensional high resolution simulation, for a variety of injected water saturations, in both secondary and tertiary displacements.

Laser-assisted atomic layer epitaxy of GaP in chemical beam epitaxy

A new atomic layer epitaxy using a photo-process without alternate gas supply in chemical beam epitaxy is proposed. The effects of ultraviolet-laser irradiation on GaP growth at low substrate temperatures were studied in detail using triethylgallium (TEGa) and PH 3. The growth rate of GaP was enhanced by ultraviolet light emitted from an N 2 laser. The growth rate increased with photon number and saturated above ∼10 17 photons cm -2 pulse. Under enough light intensity (2.7 × 10 17 photons cm -2 pulse), the growth rate was kept constant in a certain range of TEGa flow rate by N 2 laser irradiation. This result opens monolayer growth by UV-irradiation under a simultaneous supply of source gases.

Low-Temperature Metalorganic Chemical Vapor Deposition of GaAs on Si by Alternate Gas Flow of the Source Materials

GaAs layers were grown on Si substrates at 450°C by alternating the gas flow of trimethyl gallium and arsine. Raman spectra showed that the intensity of the longitudinal optical phonon peak taken from GaAs was increased by this approach. Furthermore, transmission electron microscopy showed the reduction of the lattice turbulence and many threading dislocations, which were observed in GaAs layers grown on Si without this approach.

Atomic layer epitaxy of AlAs using thermally decomposed gas molecules

A new method of atomic layer epitaxy (ALE) using a thermal-cracking tube is investigated and applied to AlAs growth. ALE growth of AlAs is accomplished in a substrate temperature range from 460 to 480 °C using an alternate gas supply of AsH3 and thermally decomposed alkylaluminum generated from trimethylaluminum (TMA). An analysis of the cracking kinetics using a quadrupole mass spectrometer reveals that ALE results from the chemisorption enhancement of column III materials related to decomposed alkylaluminum.

Metal Organic Chemical Vapor Deposition Growth of GaAs on Si Using GaAs Buffer Layer Grown by an Alternate Gas Flow of Source Materials

We tried the atomic layer epitaxy (ALE) growth of GaAs initial layer in a two-step growth of GaAs on Si by a conventional metal organic chemical vapor deposition (MOCVD) system. The etch pit density of GaAs overlayer became smaller than that without this approach. The cross sectional transmission electron microscope (TEM) of this sample indicated that the improvement of crystalline quality of GaAs overlayer was attributed to the smooth interface structure of GaAs/Si due to the layer by layer growth of the buffer layer.

Growth Rate Limiting and Carbon Reduction Processes for GaAs Grown by Alternate Gas Supply using H2 and N2 Carrier Gases

ABSTRACTProcesses limiting the growth of GaAs grown by an alternate gas supply are investigated by kinematical analysis. Based on these results, it is shown that the atomic layer epitaxial (ALE) window is expanded on the high temperature by the suppression of the decomposition of column III gas sources using a nitrogen carrier gas and on the low temperature side by the enhancement of their chemisorption to substrate surface atoms by a new method using a cracking tube. The latter enables us to achieve ALE of AlAs for the first time. Moreover, the carbon concentration is reduced by one order of magnitude by such a reaction control.

Atomic Level Control in Crystal Growth Utilizing Reconstruction of the Surface Superstructure

ABSTRACTA novel mechanism of atomic level control in crystal growth utilizing reconstruction of surface superstructures is proposed. We have found a distinguished feature of surface reconstruction during crystal growth of 3C-SiC using an alternate gas molecular beam supply of Si2H6 and C2H2. When Si2H6 is supplied, S atoms generated by thermal decomposition adsorb on the surface constructing superstructures. A fixed number of Si atoms forming surface superstructures can react with C2H2 yielding single crystalline 3C-SiC growth in the subsequent period, which realizes atomic level control in epitaxy of 3C-SiC. The reconstruction sequence is analyzed based on RHEED observations, and the obtained crystal quality is discussed.

Growth of ZnSe and ZnSSe at Low Temperature with Aid of Atomic Hydrogen and Alternate Gas Supply

ABSTRACTHigh quality ZnSe films were successfully grown on GaAs(100) at low temperatures, 200 °C or lower by Hydrogen Radical-enhanced Chemical Vapor Deposition (HRCVD). Defects were makedly eliminated by the following factors: selection of source materials; avoidance of ion bombardment; and suppression of formation of adducts by alternate gas supply. Strained-layer superlattice (SLS) consisting of ZnSe as the well and ZnS0. 1Se0.9 as the barrier was made by this technique. Emission line attributed to the free exciton was dominantly observed in the SLS.

Effect of Hydrogen on Pseudomorphic ZnSe onto GaAs by the Alternate Gas Supply of Dimethylzinc and Dimethylselenide in the MOMBE System

We investigated the pseudomorphic ZnSe on GaAs grown by the alternate gas source supply of dimethylzinc (DMZ) and dimethylselenide (DMSe) in the MOMBE system. We found through the in-situ RHEED monitoring that two-dimensional nucleation occurs from the early stage of growth if the GaAs substrates are pretreated by (NH4)2Sx solution. A growth rate of about 0.95 ML (monomolecular layer) ZnSe per one operational cycle of gas source supply could be achieved on (NH4)2Sx-pretreated GaAs substrates at 200°C under hydrogen gas exposure during growth. This result indicates that nearly complete atomic coverage is successfully proceeded in each step as a result of the termination of alkyl radicals adsorbed on the surface by hydrogen. Crystal qualities were much improved by both the substrate pretreatment and the hydrogen gas supply.

Biosampling for metal speciation

Human erythrocytes (ery's) under physiological conditions are capable of a selective uptake of dissolved chromates beside Cr(III) from aqueous solutions. For sampling the mechanical stability of the red blood cells is increased by immobilization in Ca-alginate beads without loss of the biochemical activity against Cr(VI). Radiotracer studies were performed in order to determine the influence of temperature, pH, and concentration and solubility of chromates on the accumulation, which follows a Michaelis-Menten kinetics. After sampling the ery's are separated from the gel and introduced into a multiple-step clean-up procedure preceding a GFAAS measurement of chromium. The direct determination of chromium in erythrocytes (and comparable matrices) by GFAAS is supported by the use of oxygen as alternate gas during the thermal decomposition of the samples, leading to advantages in routine analysis. The statistical parameters of this method are critically reviewed. The combination of biosampling and GFAAS represents a new way for metal speciation, especially in cases where decomposition of the analyte during standard sampling procedures is likely; this is demonstrated for Cr(III)/Cr(VI) as an example in view of immission measurements of Cr(VI) in airborne particulates.

Derivatization procedure for gas chromatographic determination of hydroxylamine

Hydroxylamine has been of special interest recently because of the possibilities of manufacturing it by using electrochemical methods in which ammonia might also be formed. Its general chemistry and applications have been described elsewhere. Presently, there are two gas chromatographic methods reported for the determination of hydroxylamine in aqueous media. The first involves reacting the hydroxylamine to form acetone oxime and subsequently injecting the aqueous solution directly into a gas chromatograph equipped with nitrogen and flame ionization detectors. The second involves oxidizing hydroxylamine to nitrous oxide and trapping the gas for determination in an electron capture equipped gas chromatograph. Limits of detection are in the micromolar range for the former and the nanomolar range for the latter. Here, an alternate gas chromatographic procedure for determining hydroxylamine as the acetone oxime is described. Neither direct aqueous injection nor elaborate instrumentation is required. Extraction of the oxime into an ether phase allows for concentrating the analyte ad facilitates the use of an internal standard. The limitations and inconveniences of direct aqueous injection are avoided included column degradation and filament burnout in mass spectrometry detectors.