Nitrogen Carrier Gas Research Articles

Dynamic vapor generator for moderate and low volatility compounds

This paper describes the development, testing and application of a device capable of dynamically generating atmospheres containing stable concentrations of moderate to low volatility organic chemicals. The generator is of simple construction, being a glass tube packed with an inert support matrix that is physically coated with the appropriate test compound to be added to the atmosphere. The packed tube is located within a temperature controlled oven (typically a gas chromatograph oven is used) and is supplied with nitrogen carrier gas which can become equilibrated with the test component under the operational conditions applied. Based upon the volatility characteristics of the test compound or compounds present in the generator, judicious choice of carrier gas flow rate and oven temperature can provide an effluent gas stream that remains stable in component concentration over extended operational periods. The device has been applied to the formation of test atmospheres containing chlorpyrifos for the purpose of testing industrial hygiene adsorbent tubes used in air monitoring procedures.

The Kinetics of Antimony Removal from Copper by Soda Injection

AbstractSodium carbonate or soda was injected into 70 kg heats of copper under controlled atmosphere at various soda ash and carrier gas flow rates. Samples were taken during injection, and analyzed for antimony and oxygen. The soda utilizations were generally less than 25% of that injected. The fraction of antimony eliminated increased with oxygen content, reaching over 90%. There was no appreciable difference in reaction rate between light and dense soda, between nitrogen and air carrier gas or between soda and sodium bicarbonate.A theoretical analysis of the kinetics of the antimony removal with soda-rich slag indicates that the rate is controlled by antimony diffusion in the metal. The measured rates were indeed partially controlled by the antimony content in the copper, but also depended on the oxygen content. This latter observation may be attributed to the presence of a cuprous oxide phase containing soda which provides a rapid, parallel reaction path. The amount of this phase increases with oxygen...

The Kinetics of Antimony Removal from Copper by Soda Injection

Sodium carbonate or soda was injected into 70 kg heats of copper under controlled atmosphere at various soda ash and carrier gas flow rates. Samples were taken during injection, and analyzed for antimony and oxygen. The soda utilizations were generally less than 25% of that injected. The fraction of antimony eliminated increased with oxygen content, reaching over 90%. There was no appreciable difference in reaction rate between light and dense soda, between nitrogen and air carrier gas or between soda and sodium bicarbonate.A theoretical analysis of the kinetics of the antimony removal with soda-rich slag indicates that the rate is controlled by antimony diffusion in the metal. The measured rates were indeed partially controlled by the antimony content in the copper, but also depended on the oxygen content. This latter observation may be attributed to the presence of a cuprous oxide phase containing soda which provides a rapid, parallel reaction path. The amount of this phase increases with oxygen content, thereby increasing the antimony removal rate. The implications of these findings for full-scale practice are discussed.

Simultaneous determination of some active ingredients in cough-cold syrups by gas-liquid chromatography

A simple, efficient and accurate gas-liquid chromatography (GLC) method for the simultaneous determination of eight active ingredients in cough-cold syrups has been developed. The active ingredients under study were bromhexine, chlorpheniramine, codeine, dextromethorphan, diphenhydramine, ephedrine/pseudoephedrine, guaiphenesin and papaverine. Before injection, the active ingredients were first separated, from the excipients present in the cough-cold syrups, with chloroform, from alkaline medium. They were then separated by GLC on a glass column (5 ft x 2 mm i.d.) packed with 3% of OV-25 supported on Supelcoport (80-100 mesh). The column temperature was maintained at 170 degrees C for 1 min, then programmed to 265 degrees C at a rate of 10 degrees C min-1, and maintained at this temperature for 10 and 1 min, respectively, for samples with and without papaverine. The flow-rate of the nitrogen carrier gas was 30 ml min-1. A flame-ionisation detector was used for detection, and clomipramine hydrochloride was used as the internal standard. The recoveries of the drugs ranged from 96.0 to 99.7%, and the relative standard deviations for ten replicate determinations ranged from 0.49 to 4.7%. Results are reported for nine commercially available cough-cold syrups.

Chemical vapour deposition of epitaxial Ni-Zn ferrite films by thermal decomposition of acetylacetonato complexes

Epitaxial (Ni, Zn)Fe2O4 films were prepared on (100) MgO single crystal substrate by lowpressure chemical vapour deposition using a thermal decomposition of acetylacetonatocomplexes, Ni(acac)2, Zn(acac)2 and Fe(acac)3. These complexes were evaporated at 157, 79 and 146° C, respectively, and transported with nitrogen carrier gas (flow rate 100 ml min−1) to the deposition furnace. Polycrystalline and epitaxial films were grown at 500 to 600 and 600 to 650° C, respectively, under a pressure of 12 torr. The epitaxial film of Ni1−xZnxFe2O4 (x⋍0.4) treated at 600° C for 60 min, showed the saturation magnetization of 67 e.m.u. g−1 and the coercive force of 20 to 30 Oe.

Regeneration of a P [sbnd]V [sbnd]O [sbnd]Zn butane oxidation catalyst using chlorine containing hydrocarbons

A fresh V P O Zn (vanadyl phosphate) catalyst has a maximum molar yield of maleic anhydride of 52% (at 450°C) which eventually becomes a spent catalyst having a maximum yield of 44% (at 400°C). This catalyst can be regenerated by passing carbon tetrachloride (in an air or nitrogen carrier gas) over its surface at 300–450°C. The products in the effluent of the reactor are consistent with the decomposition of CCl 4, (CO, CO 2, VCl 4, unknown chlorine compounds) and with part of the catalyst surface being “stripped” off (VCl 4, O 2, unknown phosphorus containing compounds). Twenty-four hours after the CCl 4 regeneration, the catalytic properties of the regenerated and fresh catalysts are identical i.e. the conversion, selectivities, yields (as a function of temperature) as well as other physical properties - surface areas, XRD patterns, and bulk P/V ratios. The experimental data is consistent with the CCl 4 selectively reacting with the poisoned sites and removing the vanadium from them by forming VCl 4. A regenerated catalyst gives a XRD pattern consisting of a mixture of the catalyst precursor and the fresh catalyst indicating a bulk rearrangement (presumably topotactic). The regeneration procedure can be practiced a large number of times without a detrimental effect on the catalytic performance.

Pyrolysis of grain screenings in a batch reactor

AbstractA preliminary study of the pyrolysis of grain screenings (wheat) has been carried out using a batch pyrolysis unit operating at atmospheric pressure. Grain screenings are the materials removed mechanically from grains (wheat, rapeseed, barley, etc.) by cleaning or separating equipment in grain elevators. Reaction conditions were varied to determine the effect of these changes on the final product (tar, gas, and char). The reaction variables manipulated included temperature (600–800°C), nitrogen carrier gas velocity, and potassium carbonate catalyst. It was found that the yields of ethylene were higher than those of ethane. These hydrocarbons were accompanied by smaller but significant yields of hydrogen and C4 to C6 hydrocarbons. The grain screenings impregnated with 15 wt% potassium carbonate catalyst gave higher synthesis gas yields with a H2/CO mole ratio up to 4.1. With the experimental set up used in the present study, the mass balances achieved were low and ranged between 65 and 77% of the weight of the grain screenings used.

Stability-indicating capillary gas—liquid chromatographic assay of dicyclomine hydrochloride in some pharmaceutical formulations

A stability-indicating assay method for some dicyclomine hydrochloride formulations was developed utilizing capillary gas—liquid chromatography. A methanolic extract of the sample, containing phenacetin as internal standard, was chromatographed by temperature programming on a 15 m × 0.524 mm I.D., DB-17 column with nitrogen carrier gas and flame ionization detection (1 · 10 −10 A). The dicyclomine hydrochloride was well resolved from phenacetin with retention times of ca. 9 and 7 min, respectively. Dicyclomine hydrochloride—internal standard peak area ratio was linear over 0.1–1.0 μg of dicyclomine hydrochloride injected ( r  0.999). Under the experimental conditions the limit of detection was 0.025 μg of dicyclomine hydrochloride injected. Validation studies with synthetic capsules, tablets and injectables covering a range of 5–25 mg of dicyclomine hydrochloride per unit gave an overall percent recovery (± relative standard deviation, n  9) of 99.9 ± 1.7%. The method was successfully applied to the assay of commercial formulations. Stability tests indicated that degradation products of dicyclomine, formed upon acid treatment, did not interfere with the dicyclomine and internal standard peaks. They further showed that dicyclomine is fairly stable in base.

Adsorption on film-free and antibody-coated piezoelectric sensors

Frequency responses associated with adsorption of gas-phase toluene, o-nitrotoluene, valproic acid and the pesticides parathion, malathion and disulfoton on uncoated and protein-coated piezoelectric sensors are reported. Valproic acid antiserum and antibody against parathion were included among the set of protein films studied. Responses, which were reversible in all cases, are attributed to chemisorption or physisorption on electrode and protein surfaces. Under the conditions used, no signals corresponding to selective immunochemical binding were found. Highly sensitive responses of protein-coated sensors to the pesticide species were confirmed, with the lower limit of detection being about 0.01 μg l −1 in nitrogen carrier gas.

Interaction of ethylene glycol with alumina supported copper —an FTIR study

AbstractThe adsorption of ethylene glycol on γ‐alumina as well as on an alumina‐supported copper catalyst has been studied under working conditions using transient FTIR experiments. Time‐dependent spectra were recorded after exposure of the substrates to a pulse of ethylene glycol, or to subsequent stepwise increases in the ethylene glycol concentration. On alumina both dehydration and dehydrogenation products were observed; on supported copper dehydration was suppressed and only the aldehyde formed by dehydrogenation of the reactant glycol was observed. Hydrogen was found to prevent the formation of dialdehydic species (surface bound glyoxal) which were observed in nitrogen carrier gas. The relevance of these results to the mechanism of the copper‐catalyzed amination of alcohols is discussed.

Atomic absorption spectrometric determination of gasoline additives by vapour phase sample introduction

An atomic absorption spectrometric method has been used for the determination of lead and manganese additives in gasolines. Using a pre-heated Pyrex reactor, gasoline samples and standards are volatilised and introduced into the flame, in the vapour phase, by a nitrogen carrier gas flow. The detection limit for manganese with this method is 0.3–1 p.p.m. and in the order of 2 p.p.m. for lead. Results obtained for the analysis of commercial gasoline samples by the recommended procedure are compared with a reference method. Results for manganese additives are similar to those obtained through emulsification of the samples. For lead additives it is necessary to use a calibration graph prepared for samples of the same type which had been analysed previously. For this reason caution must be taken in applying the method indiscriminately to the determination of lead in gasoline from sources which have not been characterised.

Infrared gas analysis of both gaseous and dissolved CO2 in small‐volume marine samples1

A simple, inexpensive infrared gas analysis system for use with small‐volume marine samples has been developed. The method involves injecting between 10 and 250 µl of a seawater sample onto an acidified gas‐stripping column. The CO2 released is transported via a nitrogen carrier gas to an infrared gas analyzer. The C.V. from seven replicate injections of a 1.0 mM Na2CO3 solution ranged from <0.3% to 1.8% depending on sample size.Evacuated blood collection tubes were used to collect and store aqueous and gaseous samples in the laboratory and field. Aqueous samples were preserved with chloroform to eliminate the possibility of changes following collection. The results indicate that samples collected in this manner can be stored for 4 weeks before analysis and that the method is efficient and cost‐effective.

Intraparticle diffusion coefficients in packed columns: Measurement by arrested‐flow gas chromatography

AbstractArrested‐flow chromatography was used to determine intraparticle diffusivities of large‐pore particles packed in columns. Particle and column tortuosity factors were determined for helium tracer in nitrogen carrier gas at 40°C and atmospheric pressure. Semiempirical modifications of Maxwell's, Burger's, Jeffrey's, and Rayleigh's relations for the composite diffusivity of spherical particles in a stationary medium are proposed for the effective composite diffusion coefficient for a packed bed of porous particles. The equations, modified to represent accurately the extraparticle void diffusion based on measurements for beds of nonporous particles, are used to evaluate intraparticle diffusivities from experimental data obtained by arrested‐flow chromatography.

Mass spectrometric measurements of the negative ions formed in the thermionic ionization detector with nitrogen carrier gas

A specialized ion source for an atmospheric pressure ionization mass spectrometer was constructed so that ionizing conditions within it were identical to those existing within the nitrogen carrier gas mode of the thermionic ionization detector for gas chromatography. During the passage of several substituted nitrobenzenes through this ion source, an effort was made to identify the negative ions which are thought to be responsible for this detector's response. For all compounds studied no negative ions having masses within the 1–500 a.m.u. mass range of the mass spectrometer were detected. However, negative ions of unknown masses greater than 500 a.m.u. were detected in each case. This unexpected result provides additional basis for speculation concerning the mechanism of response of the thermionic ionization with nitrogen mode.

薄膜の形成と構造 アセチルアセトナト（ａｃａｃ）錯体の熱分解ＣＶＤによる（Ｍｎ，Ｚｎ）Ｆｅ２Ｏ４膜の合成

Polycrystalline (Mn, Zn)Fe2O4 films were prepared on silica glass substrate by CVD using three kinds of acetylacetonatocomplexes, Mn(acac)2, Fe(acac)3 and Zn(acac)2.H2O as starting materials. These complexes were evaporated at a reduced total pressure of 10 Torr and at temperatures of 205°C, 140-150°C and 85°C, respectively and transported with nitrogen carrier gas to the deposition zone. The growth conditions and magnetic properties of the polycrystalline (Mn, Zn)Fe2O4 films were as follows. deposition temperature: 500-600°C, oxygen gas flow rate: 10 ml/min, reaction time: 20 min, saturation magnetization: 50 emu/g, coercive force: 80 Oe and Curie temperature: 270°C.

Growth of GaN films using trimethylgallium and hydrazine

Hydrazine has been used as a nitrogen source for the organometallic vapor phase deposition of GaN using trimethylgallium and a nitrogen carrier gas in the temperature range 425–960 °C. Hydrazine and trimethylgallium form an adduct at room temperature which decomposes over the substrate with an activation energy of 1 eV for temperatures below 650 °C. No carbon has been detected by Auger spectroscopy in the films. The electrical properties are dominated by oxygen impurities, probably originating from the hydrazine. Since hydrazine readily decomposes above 400 °C, it is a better source of nitrogen for low-temperature depositions than other, more stable nitrogen sources.

Generation, behavior, and toxicity of ammonium sulfite aerosols.

Ammonium sulfite aerosols were continuously generated for periods up to 6 h by gas phase reaction of sulfur dioxide, ammonia, and water vapor in nitrogen carrier gas. Concentrations from 1 to 500 mg/m3 were obtained. Aerosol leaving the generator was greater than 90% sulfite, but when diluted with air preparatory to animal exposures, the aerosol was rapidly oxidized. Sulfite concentrations in a large exposure chamber with a long residence time were consistently less than 25 percent of the aerosol mass. Sulfite concentrations in a nose-only or head-only inhalation chamber 1 ft downstream from a radial air injection system ranged from 10 to 80 percent sulfite. The latter system, with a short residence time, was used to expose animals to aerosols. Effects of the mixed sulf ite/sulfate aerosol on acute mortality of guinea pigs and tracheal mucous clearance of dogs were measured and no effects were observed.

Lubrication from the Vapor Phase at High Temperatures

Vapor phase lubrication has been demonstrated using a conventional four-ball wear Lester run at 370°C using M50 hot hardness steel ball bearings. The four-ball wear tester was modified to control both the temperature and the environment surrounding the ball pot and spindle. The lubricant in all cases comprised a homogeneous gas phase mixture of nitrogen and phosphate ester vapors. The two phosphate esters used were tributyl phosphate (TBP) and tricresyl phosphate (TCP). The volume percent phosphate ester vapor in nitrogen ranged from 0.10 to 6.0 percent. The minimum temperature of the four balls was maintained at 370°C which was always at least 50°C higher than the temperature of the homogeneous vapors delivered so that there was no possibility of vapor condensation on the wear contacts. Vapor phase lubrication by phosphate esters appears to be as effective at a bulk temperature of 370°C as typical nonadditive mineral oils are in the liquid state at room temperature to 75°C. For example, TCP delivered from the vapor phase could support loads up to 50 kg at a lubricant concentration of only 0.5 percent. Scanning electron microscopic (SEM) pictures of a steel surface at 600°C delivered with 1.2 percent TBP in a nitrogen carrier gas show large amorphous like structures. This suggests that the deposited lubricating film exists as a polymer of the original TBP in a liquidlike state at this temperature. On cooling to room temperature, section of the film apparently coalesced giving he coaling observed. Such fluidity of the lubricating film at high temperatures would be particularly valuable in metal-forming operation.

Transmission of water through a biocompatible polyurethane: application to circulatory assist devices.

The permeability characteristics of a water-segmented polyurethane (Biomer) system under the conditions encountered in circulatory-assist devices were investigated. A diffusion cell and permeability system providing precise control of membrane boundary conditions and allowing continuous measurement of water vapor transmission was designed. Liquid water at 37 degrees C was used as the donor fluid and the system incorporated a constant-flow nitrogen carrier gas and an optical dew point sensor downstream to determine the water vapor mass flow rate as a function of time. The mass flow rate was then numerically integrated and plotted against time to allow calculation of effective diffusion coefficient (D) by the dynamic time lag method. Steady-state permeabilities were found to be insensitive to donor chamber hydrostatic pressure (50-200 mm Hg) indicating that bulk flow is not a transport mechanism in these membranes. The permeability coefficient (P) was independent of membrane thickness (H) over the four samples tested (0.0102, 0.0148, 0.0269, and 0.0366 cm), with an average value of 3.29 X 10(-4) cm2/s. Thus, diffusion was Fickian with negligible boundary layers. A plot of lag time versus H2 was linear (R = 0.98) yielding a value for D of 2.18 X 10(-7) cm2/s. A water-Biomer partition coefficient was determined for each sample with an average value of 1525, indicating a moderately hydrophilic membrane with a water sorption of 6.3% at 37 degrees C. Since water transport is by Fickian diffusion in the absence of bulk flow, liquid water cannot be expected to accumulate in circulatory-assist devices unless a condensing surface is maintained within the system.

Microassay for ammonium by determination of ammonia nitrogen in a nitrogen analyzer

The method described comprises the transformation of ammonium into ammonia, the rapid and gentle liberation of the ammonia followed by the measurement of the nitrogen in a Dohrmann nitrogen analyzer. Untreated biological samples (1–50 μl) were pipetted onto magnesium oxide tablets at 130°C and the ammonia liberated was transferred by a continuous stream of nitrogen carrier gas into the nitrogen analyzer. There the ammonia was determined by oxidative pyrolysis and subsequent chemiluminescence measurement of the excited NO 2. The result could be read in nanograms ammonia nitrogen within 6.5 min. Apart from volatile amines, which are usually negligible in biological samples, the method was specific for ammonia because under the given conditions of volatilization the labile groups of glutamine and asparagine did not interfere. The assay was sensitive in the range of 1.5–150 nmol ammonia and suitable for the routine analysis of small samples.