Stream Of Dry Nitrogen Research Articles

The physico-geometrical reaction pathway and kinetics of multistep thermal dehydration of calcium chloride dihydrate in a dry nitrogen stream.

Several inorganic hydrates exhibit reversible reactions of thermal dehydration and rehydration, which is potentially applicable to thermochemical energy storage. Detailed kinetic information on both forward and reverse reactions is essential for refining energy storage systems. In this study, factors determining the reaction pathway and kinetics of the multistep thermal dehydration of inorganic hydrates to form anhydride via intermediate hydrates were investigated as exemplified by the thermal dehydration of CaCl2·2H2O (CC-DH) in a stream of dry N2. The formation of CaCl2·H2O (CC-MH) as the intermediate hydrate is known during the thermal dehydration of CC-DH to form its anhydride (CC-AH). However, the two-step kinetic modeling based on the chemical reaction pathway considering the formation of the CC-MH intermediate failed in terms of the reaction stoichiometry and kinetic behavior of the component reaction steps. The kinetic modeling was refined by considering the physico-geometrical reaction mechanism and the self-generated reaction conditions to be a three-step reaction. The multistep reaction was explained as comprising the surface reaction of the thermal dehydration of CC-DH to CC-AH and subsequent contracting geometry-type reactions from CC-DH to CC-MH and from CC-MH to CC-AH occurring consecutively in the core of the reacting particles surrounded by the surface product layer of CC-AH. The acceleration of the linear advancement rate of the reaction interface during both contracting geometry-type reactions was revealed through multistep kinetic analysis and was described by a decrease in the water vapor pressure at the reaction interface as the previous reaction step proceeded and terminated.

Untrapping Kinetically Trapped Ions: The Role of Water Vapor and Ion-Source Activation Conditions on the Gas-Phase Protomer Ratio of Benzocaine Revealed by Ion-Mobility Mass Spectrometry.

The role of water vapor in transforming the thermodynamically preferred species of protonated benzocaine to the less favored protomer was investigated using helium-plasma ionization (HePI) in conjunction with ion-mobility mass spectrometry (IM-MS). The IM arrival-time distribution (ATD) recorded from a neat benzocaine sample desorbed to the gas phase by a stream of dry nitrogen and ionized by HePI showed essentially one peak for the O-protonated species. However, when water vapor was introduced to the enclosed ion source, within a span of about 150 ms the ATD profile changed completely to one dominated by the N-protonated species. Under spray-based ionization conditions, the nature and composition of the solvents have been postulated to play a decisive role in defining the manifested protomer ratios. In reality, the solvent vapors present in the ion source (particularly the ambient humidity) indirectly dictate the gas-phase ratio of the protomers. Evidently, the gas-phase protomer ratio established at the confinement of the ions is readjusted by the ion-activation that takes place during the transmission of ions to the vacuum. Although it has been repeatedly stated that ions can retain a "memory" of their solution structures because they can be kinetically trapped, and thereby represent their solution-based stabilities, we show that the initial airborne ions can undergo significant transformations in the transit through the intermediate vacuum zones between the ion source and the mass detector. In this context, we demonstrate that the kinetically trapped N-protomer of benzocaine can be untrapped by reducing the humidity of the enclosed ion source. Graphical Abstract ᅟ.

A new method for calibrating hygrometers.

In this study, a new method was proposed for calibrating hygrometers. The moisture permeation cylinder, which was used to measure the water vapor permeability of fabrics, was used to generate various levels of relative humidity. A dry nitrogen stream was employed to sweep the water vapor away. It was deduced that the relative humidity of the outgoing nitrogen stream was negatively correlated to the volumetric flow rate of nitrogen stream, i.e., the lower the volumetric flow rate, the higher the relative humidity. The hygrometer HMT 333 was chosen to measure the relative humidity of the outgoing nitrogen stream at five levels. The test data indicated that good agreement was observed between the measured humidity and the observed humidity from the Vaisala, Inc. Moreover, this method offers high sensitivity and fast response. Therefore, the relative humidity of the outgoing nitrogen stream can be used as a secondary humidity reference.

Apolipoprotein E3 (ApoE3) but Not ApoE4 Protects against Synaptic Loss through Increased Expression of Protein Kinase Cϵ

Synaptic loss is the earliest pathological change in Alzheimer disease (AD) and is the pathological change most directly correlated with the degree of dementia. ApoE4 is the major genetic risk factor for the age-dependent form of AD, which accounts for 95% of cases. Here we show that in synaptic networks formed from primary hippocampal neurons in culture, apoE3, but not apoE4, prevents the loss of synaptic networks produced by amyloid β oligomers (amylospheroids). Specific activators of PKCε, such as 8-(2-(2-pentyl-cyclopropylmethyl)-cyclopropyl)-octanoic acid methyl ester and bryostatin 1, protected against synaptic loss by amylospheroids, whereas PKCε inhibitors blocked this synaptic protection and also blocked the protection by apoE3. Blocking LRP1, an apoE receptor on the neuronal membrane, also blocked the protection by apoE. ApoE3, but not apoE4, induced the synthesis of PKCε mRNA and expression of the PKCε protein. Amyloid β specifically blocked the expression of PKCε but had no effect on other isoforms. These results suggest that protection against synaptic loss by apoE is mediated by a novel intracellular PKCε pathway. This apoE pathway may account for much of the protective effect of apoE and reduced risk for the age-dependent form of AD. This finding supports the potential efficacy of newly developed therapeutics for AD.

The Vitamin K-dependent Carboxylase Generates γ-Carboxylated Glutamates by Using CO2 to Facilitate Glutamate Deprotonation in a Concerted Mechanism That Drives Catalysis

The γ-glutamyl carboxylase converts Glu to carboxylated Glu (Gla) to activate a large number of vitamin K-dependent proteins with diverse functions, and this broad physiological impact makes it critical to understand the mechanism of carboxylation. Gla formation is thought to occur in two independent steps (i.e. Glu deprotonation to form a carbanion that then reacts with CO(2)), based on previous studies showing unresponsiveness of Glu deprotonation to CO(2). However, our recent studies on the kinetic properties of a variant enzyme (H160A) showing impaired Glu deprotonation prompted a reevaluation of this model. Glu deprotonation monitored by tritium release from the glutamyl γ-carbon was dependent upon CO(2), and a proportional increase in both tritium release and Gla formation occurred over a range of CO(2) concentrations. This discrepancy with the earlier studies using microsomes is probably due to the known accessibility of microsomal carboxylase to water, which reprotonates the carbanion. In contrast, tritium incorporation experiments with purified carboxylase showed very little carbanion reprotonation and consequently revealed the dependence of Glu deprotonation on CO(2). Cyanide stimulated Glu deprotonation and carbanion reprotonation to the same extent in wild type enzyme but not in the H160A variant. Glu deprotonation that depends upon CO(2) but that also occurs when water or cyanide are present strongly suggests a concerted mechanism facilitated by His-160 in which an electrophile accepts the negative charge on the developing carbanion. This revised mechanism provides important insight into how the carboxylase catalyzes the reaction by avoiding the formation of a high energy discrete carbanion.

A Microdrop Generator for the Calibration of a Water Vapor Isotope Ratio Spectrometer

Abstract A microdrop generator is described that produces water vapor with a known isotopic composition and volume mixing ratio for the calibration of a near-infrared diode laser water isotope ratio spectrometer. The spectrometer is designed to measure in situ the water vapor deuterium and oxygen (17O and 18O) isotope ratios from the low troposphere up to the lower stratosphere with a high temporal resolution, and is based on ultrasensitive optical-feedback cavity-enhanced absorption spectroscopy. To calibrate the spectrometer, a commercial microdrop generator (Microdrop GmbH) is used to inject water droplets of known size at a preset repetition frequency into a stream of dry nitrogen or synthetic air. Complete evaporation of the small droplets ensures that there is no isotopic fractionation between the liquid phase and the generated moist “air.” The water mixing ratio of the synthetic air is controlled by the repetition rate and gas flow. The current system spans a water mixing ratio range from about 10 to 5000 ppmv, representing the range of conditions expected in the lower to upper troposphere. Both lower and higher mixing ratios can be produced after small modifications to the injector’s operating conditions or the system’s design.

Lipids of human meibum: mass-spectrometric analysis and structural elucidation

The purpose of this study was to structurally characterize the major lipid species present in human meibomian gland secretions (MGS) of individual subjects by means of ion trap atmospheric pressure ionization mass spectrometry analysis (API MS(n)). The samples of MGS and authentic lipid standards were analyzed in direct infusion and high-pressure liquid chromatography (HPLC) experiments with API MS(n) detection of the analytes (HPLC API MS(n)). The major precursor ions were isolated and subjected to further sequential fragmentation in MS(n) experiments, and their fragmentation patterns were compared with those of authentic lipid standards. Multiple precursor ions were observed in the positive-ion mode. Among those, previously identified cholesterol (Chl; m/z 369; [M - H(2)O + H](+)) and oleic acid (OA; m/z 283; [M + H](+)) were found. The other major compounds of the general molecular formula C(n)H(2n-2)O(2) were consistent with wax esters (WEs), with OA as fatty acyl component. Accompanying them were two homologous series of compounds that fit the molecular formulas C(n)H(2n-4)O(2) and C(n)H(2n)O(2). Subset 2 was found to be a homolog series of linoleic acid-based WEs, whereas subset 3 was, apparently, a mixture of stearic acid-based WEs. HPLC API MS(n) analysis revealed the presence of large quantities of cholesteryl esters (Chl-Es) in all of the tested samples. Less than 0.1% (w/w) of oleamide was detected in human MGS. In the negative-ion mode, three major compounds with m/z values of 729, 757, and 785 that were apparently related to anionogenic lipids of the diacylglyceryl family were found in all of the samples. Common phospholipids and ceramides (Cers) were not present among the major MGS lipids. Phosphocholine-based lipids were found in MGS in quantities less than 0.01% (w/w), if at all. This ratio is two orders of magnitude lower than reported previously. These observations suggest that MGS are a major source of nonpolar lipids of the WE and Chl-E families for the tear film lipid layer, but not of its previously reported (phospho)lipid, Cer, and fatty acid amide components.

Optimisation of analytical method for estrogen in surface water and primary risk assessment in South Creek

A very non-polar sorbent, polystyrene-divinyl-benzene (brand: biobeads supplied by BioRad, with 30∼50 mesh) was tested for its extraction efficiency of four target compounds, estrone, estradiol, ethynylestradiol and estriol, from larger volumes (8 l) of water samples. To achieve adequate sensitivity of instrumental analysis by GC/MS, an improved estrogen derivatisation method was developed. For the simultaneous determination of the four estrogens, 50 ?l BSTFA+1% TMCS and 50 ?l pyridine was used for the derivatisation. Ions of different masses, 342 for estrone and 425 for 17α-ethynylestradiol, were formed using this protocol. The residual derivatisation reagents and pyridine were completely removed under a stream of dry nitrogen. Using the optimised extraction and derivatisation protocol, estrogen levels in the South Creek in Sydney and the Emigrant Creek in North of New South Wales were analysed. The possible contribution of the discharges from wastewater treatment plant as a source of estrogens is discussed.

UVphotolysis of the binary mixtures of VOCs in dry nitrogen stream

The effect of H/Cl atomic ratio on the relative contribution of direct photolysis and reactions based on •Cl radical to the photodecomposition of chlorinated methanes was investigated in their binary mixtures.

Detection and Quantification of Protein Biomarkers from Fewer than 10 Cells

The use of antibody microarrays continues to grow rapidly due to the recent advances in proteomics and automation and the opportunity this combination creates for high throughput multiplexed analysis of protein biomarkers. However, a primary limitation of this technology is the lack of PCR-like amplification methods for proteins. Therefore, to realize the full potential of array-based protein biomarker screening it is necessary to construct assays that can detect and quantify protein biomarkers with very high sensitivity, in the femtomolar range, and from limited sample quantities. We describe here the construction of ultramicroarrays, combining the advantages of microarraying including multiplexing capabilities, higher throughput, and cost savings with the ability to screen very small sample volumes. Antibody ultramicroarrays for the detection of interleukin-6 and prostate-specific antigen (PSA), a widely used biomarker for prostate cancer screening, were constructed. These ultramicroarrays were found to have a high specificity and sensitivity with detection levels using purified proteins in the attomole range. Using these ultramicroarrays, we were able to detect PSA secreted from 100 LNCaP cells in 3 h and from just four LNCaP cells in 24 h. Cellular PSA could also be detected from the lysate of an average of just six cells. This strategy should enable proteomic analysis of materials that are available in very limited quantities such as those collected by laser capture microdissection, neonatal biopsy microspecimens, and forensic samples.

Silicon determination in Portland cement by fluoride generation, using flame atomic absorption spectrometry

A new method for the determination of silicon in Portland cement, based on the generation of volatile species without sample pre-treatment, is proposed. The method reduces operational complexity and time without loss of precision and with similar accuracy as the current methods. It employs microwave-assisted (domestic microwave oven) digestion to produce volatile silicon fluorides by reaction of the sample with a fluorinated salt (CaF 2) in the presence of H 2SO 4 (98% w/w), using a Teflon® (PFA) reactor. The volatile fluorides are flushed out by a dry nitrogen stream and collected in 0.3 mol l −1 NaOH solution where they dissolve. Silicon is determined in this solution by flame atomic absorption spectrometry (FAAS). The recoveries are between 98 and 102%, and the precision is better than 2.5% relative standard deviation (R.S.D).

Single-use phosphorimetric sensor for the determination of nalidixic acid in human urine and milk.

A single-use phosphorimetric sensor to determine the germicide nalidixic acid is proposed. The sensing action is based on the absorption of the analyte into the sensing zone and the subsequent measurement of the phosphorescence intensity emitted by the analyte fixed in the sensor. This plane drop sensor is made up of a 3 x 1.6 cm sheet of the polyester Mylar as solid support, and a circular film 5 mm in diameter and 20 microns in thickness, formed by poly(vinyl chloride) and tributyl phosphate as the plasticizer, adhered to its surface. The sensor is introduced for 2 h into the sample solution, after which it is dried and the phosphorescence intensity is measured directly at lambda ex = 332 nm, lambda em = 412 nm, with a delay time of 0.15 ms and a gate time of 10 ms, under a dry nitrogen stream. The characteristic parameters of the construction of the sensing zone and of the processes of fixing the analyte along with the emission of phosphorescence were studied. The applicable concentration range was from 60 to 1500 ng ml-1, with a detection limit of 20 ng ml-1 and a precision of 2% expressed as relative standard deviation. The method was applied to the determination of nalidixic acid in milk and human urine with recoveries ranging between 96.0 and 103.7%. The calibration process was carried out by applying a mathematical method of finite elements that expresses the analytical signal as a function of the analyte concentration and equilibration time between the sensor and the sample solution.

Interaction of Chlorinated Ethylenes with Chromium Exchanged Zeolite Y: Anin SituFT-IR Study

The interaction of chlorinated ethylenes (vinyl chloride, 1,1 dichloroethylene, trichloroethylene, and perchloroethylene) with the surface of chromium exchanged zeolite Y (Cr–Y) catalyst has been studied byin situFT-IR spectroscopy. The adsorptions were carried out on thein situoxidized Cr–Y pellet at temperatures between 25 and 300°C in a dry nitrogen stream as a means of studying possible decomposition intermediates. The adsorption at 25°C was chiefly physical in nature although some dechlorination of the molecule was evident even at this temperature. At higher temperatures, between 100 and 300°C, an oxygen attack on the adsorbed molecule led to the formation of partially and/or fully oxygenated (but still adsorbed) species. These oxygenated species, including carboxylate and carbonate, were found to contain fewer chlorine atoms than the original feed molecule. The catalytic activity for the formation of these intermediates was found to diminish with increasing chlorine content of the feed molecule. Based on these results, a reaction pathway for the progressive catalytic oxidation of chlorinated ethylenes has been proposed.

Method for the Determination of Captan Metabolites in Milk and Bovine Tissue Samples by Gas Chromatography with Mass-Selective Detection

A method for the simultaneous determination of residues of five possible metabolites of captan, 1,2,3,6-tetrahydrophthalimide (THPI), cis-3-hydroxy-1,2,3,6-tetrahydrophthalimide (C3), cis-5-hydroxy-1,2,3,6-tetrahydrophthalimide (C5), trans-3-hydroxy-1,2,3,6-tetrahrahydrophthalimide (T3), and trans-5-hydroxy-1,2,3,6-tetrahydrophthalimide (T5), has been developed. Tissue and milk samples are macerated with acetone and centrifuged. An aliquot of the extract is diluted with ethyl acetate, and the solution is dried over anhydrous sodium sulfate. The residuum obtained after evaporation of the solvent under a stream of dry nitrogen is partitioned between hexane and acetonitrile to remove lipids. After a silica column cleanup, the metabolites are derivatized by heating with N,O-bis(trimethylsilyl)trifluoroacetamide containing 10% trimethylchlorosilane. The trimethylsilyl derivatives are quantitated by gas chromatography with mass-selective detection. The mean recoveries and coefficients of variation (CV) from the analysis of 145 fortified milk, fat, kidney, liver, and muscle samples were as follows : THPI, 91.1% (CV 15) ; T3, 93.4% (CV 16) ; T5, 92.6% (CV 17) ; C3, 95.1% (CV 14) ; and C5, 88.5% (CV 19), respectively. The fortification levels ranged from 0.01 to 1.0 μg/g.

Synthesis, isolation, and structure of an LDA-THF complex

Crystals of a dimeric 1:1 LDA-THF complex are prepared as described. A single crystal of this substance was subjected to X-ray diffraction analysis while being maintained at ∼-100 o C in a stream of dry nitrogen. The crystalline LDA-THF aggregate is a bis-solvated dimer

Drying of Beulah-Zap lignite

Lignite dried in a stream of dry nitrogen at moderate temperatures (20–80 °C) loses water in two distinguishable modes. The first mode represents about 80–85% of the loss of moisture. The second represents the other 15–20% lost under these conditions. The rate follows a unimolecular mechanism (like radioactive decay) for each mode. The activation energy for the first mode is close to the heat of vaporization of water. The rate is dependent upon the gas flow around the sample and the weight (or thickness) of the sample. Work at Amoco Oil Company indicated that the oil yield was higher for the dried coal than for raw or partly dried lignite. Work at Southern Illinois University showed that the mechanism was the same when differential scanning calorimetry was used to follow the kinetics of drying. Other work at the University of Southern Mississippi showed that the physical structure of the lignite (measured by X-ray diffraction) is measurably different for the dried and raw materials.

Room-temperature phosphorimetric determination of biogenic indole compounds adsorbed on a thin-layer chromatographic plate

A simple and sensitive method is described for the determination of biogenic indole compounds adsorbed on cellulose or alumina plates for thin-layer chromatography by room-temperature phosphorimetry. The optimum conditions were investigated for 5-hydroxyindole-3-acetic acid and indole-3-acetic acid. The compounds are spotted on the plates, which are then sprayed successively with sodium citrate or sodium acetate, and sodiu iodide solutions. The plates are dried completely under a stream of dry nitrogen, and immediately dipped in molten paraffin. The phosphorescence is stable for at least 3 h even in moist air. The limits of detection for nine biogenic indole compounds tested are between 2 and 300 pmol per sample spot.

Bonded-phase extraction column isolation of organic compounds in groundwater at a hazardous waste site

A procedure for isolation of hazardous organic compounds from water for gas chromatography/mass spectrometry analysis is presented and applied to creosote- and pentachlorophenol-contaminated groundwater resulting from wood-treatment processes. This simple procedure involved passing a 50-100 mL sample through a bonded-phase extraction column, eluting the trapped organic compounds from the column with 2-4 mL of solvent, and evaporating the sample to 100 micro-L with a stream of dry nitrogen, after which the sample was ready for gas chromatography/mass spectrometry analysis. Representative compounds indicative of creosote contamination were used for recovery and precision studies from the cyclohexyl-bonded phase. Recovery of these compounds from n-octyl-, n-octadecyl-, cyclohexyl-, and phenyl-bonded phases was compared. The bonded phase that exhibited the best recovery and least bias toward acidic or basic compounds was the n-octadecyl phase. Detailed compound identification is given for compounds isolated from creosote- and pentrachlorophenol-contaminated groundwater using the cyclohexyl-bonded phase. 12 references, 1 figure, 4 tables.

Chemical kinetics and diffusion in poly(butylene terephthalate) solid‐state polycondensation: Experiments and theory

AbstractPostpolymerization was obtained in solid PBT sheets, by annealing in a dry nitrogen stream at 214°C. After different reaction times, the samples were cut into thin slices. The Mw profile within the sample was obtained through intrinsic viscosity measurements in a phenol–TCE mixture. At each location inside the sample, the [η] vs. time curve typically shows a maximum, which is rather broad at the midplane and much sharper at the external surface. The phenomenon was mathematically described by accounting for both diffusion and chemical reactions within the slab; five simultaneous chemical reactions have been considered. The observed behavior is found to be essentially due to two competing processes, i.e., the diffusion of the low molecular weight species generated during the polycondensation and the thermal degradation reaction. The model predictions are compared with the experimental data showing a satisfactory agreement.

Nylon 6 polymerization in the solid state

AbstractThe postcondensation of nylon 6 in the solid state was studied. The reactions were carried out on fine powder in a fluidized bed reactor in a stream of dry nitrogen in the temperature range 110–205°C and during 1–24 h. The solid‐state polymerization (SSP) did not follow melt kinetics, but was found to be limited by the diffusion of the autocatalyzing acid chain end group. Factors thought to influence SSP were studied, e.g., heat treatment, starting molecular weight, and remelting. Surprisningly, heat treatment had little effect, but the starting molecular weight had a strong effect on the reaction rate. The higher the starting molecular weight, the faster the reaction. This could be explained as a changing concentration distribution of the reactive groups in the solid state on SSP. The kinetics of the SSP had more than one region, and the rate of reaction for conversions of over 30% could be expressed as − dc/dt = k(c/t), where k is a dimensionless constant independent of temperature with a value of 0.28. The integrated form has the form − In(c/co) = k In(t/τ), where co is the acid end‐group concentration at the start, t is the reaction time, and τ is the induction time. The value of τ is both dependent on the starting concentration co and the reaction temperature and has an activation energy of 105 kJ/mol.