Gas chromatographic determination of two isosorbide mononitrates in plasma

A GC/EC method has been developed for the determination of 2-isosorbide mononitrate (2-ISMN) and 5-isosorbide mononitrate (5-ISMN) in blood plasma. The procedure is based on extraction of ammonium sulfate-treated plasma with ether followed by a cleanup via n-heptane/methanol partitioning. After conversion to t-butyldimethylsilyl ethers, the ISMNs are chromatographed on a 3% OV-17 column. Absolute recoveries of 76.7 and 84.8% were achieved for 2-ISMN and 5-ISMN, respectively. Using o-nitrobenzyl alcohol as an internal standard, relative standard deviations of 4.8 to 6.1% were observed over the concentration ranges of 10 to 100 ng/ml for 2-ISMN and 250 to 1500 ng/ml for 5-ISMN.     

Extraction of Oil from Flaxseed (<Emphasis Type="Italic">Linum usitatissimum</Emphasis> L.) Using Enzyme-Assisted Three-Phase Partitioning

In this study, enzyme-assisted three-phase partitioning (EATPP) was used to extract oil from flaxseed. The whole procedure is composed of two parts: the enzymolysis procedure in which the flaxseed was hydrolyzed using an enzyme solution (the influencing parameters such as the type and concentration of enzyme, temperature, and pH were optimized) and three-phase partitioning (TPP), which was conducted by adding salt and t-butanol to the crude flaxseed slurry, resulting in the extraction of flaxseed oil into alcohol-rich upper phase. The concentration of t-butanol, concentration of salt, and the temperature were optimized to maximize the extraction yield. Under optimized conditions of a 49.29 % t-butanol concentration, 30.43 % ammonium sulfate concentration, and 35 °C extraction temperature, a maximum extraction yield of 71.68 % was obtained. This simple and effective EATPP can be used to achieve high extraction yields and oil quality, and thus, it is potential for large-scale oil production.     

制备条件对异丁烯选择性氧化催化剂性能的影响

通过正交实验设计，改变钼酸铵溶液的质量分数、pH值和催化剂焙烧温度，利用共沉淀法制备了一系列Mo-Bi-Co-Fe-Ce-Cs-K复合氧化物催化剂。借助于BET、TG-DSC、XRD等分析方法对催化剂的物理化学性质进行了表征。在常压连续流动固定床反应器中，系统地考察了上述三种制备条件对复合氧化物催化剂催化异丁烯选择性氧化生成甲基丙烯醛反应性能的影响。结果表明，大比表面积的催化剂具有较高的活性，而平均孔径小的催化剂选择性较差。 催化剂的最佳制备条件为： 钼酸铵溶液的质量分数10%、 pH值2～3、 焙烧温度500 ℃。在异丁烯∶空气=6∶94（体积比）、GHSV=3 600 h－1和360 ℃条件下，异丁烯转化率87.2％，甲基丙烯醛选择性72.0％，甲基丙烯醛收率62.7％。     

Stimulatory Effect of Different Lignocellulosic Materials for Phenolic Compound Production and Antioxidant Activity from Inonotus obliquus in Submerged Fermentation

White-rot fungus Inonotus obliquus grown in submerged culture produces antioxidative phenolic compounds. In this study, addition of lignocellulosic materials into the liquid culture increased the production and antioxidant activity of extra- and intra-cellular phenolic compounds (EPC and IPC, respectively). The production of EPC and IPC was significantly enhanced by wheat straw (by 151.2 and 45.3 %), sugarcane bagasse (by 106.9 and 26.1 %), and rice straw (by 67.6 and 38.9 %). Both of the EPC and IPC extracts from the three substrates showed a higher hydroxyl and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity than those from the control medium. The highly active polyphenols such as tea catechins of epicatechin-3-gallate (ECG) and epigallocatechin-3-gallate (EGCG), and phelligridin G in the EPC extracts increased by 113.1, 75.0, and 86.3 % in the sugarcane bagasse medium. Davallialactone and inoscavin B in the EPC extracts were generated in large amounts in the lignocellulose media but not found in the control medium. The IPC extract from the wheat straw medium had the highest production of EGCG and ECG (17.6 and 18.1 mg/l). The different enhancement among the materials was attributed to the content and degradation rate of cellulose, hemicellulose, and lignin. The different antioxidant activity of the EPC and IPC extracts was related to their phenolic compositions.     

Conversion of Magnus salt into diamminedichloroplatinum(II) isomers in aqueous solution

The conditions inducing conversion of Magnus salt into diamminedichloroplatinum(II) isomers were studied. Syntheses of cis-diamminedichloroplatinum(II) and trans-diamminedichloroplatinum(II), which are used to prepare potassium or ammonium amminetrichloroplatinate(II), are described. The identity and structure of diamminedichloroplatinum(II) isomers were verified by elemental analysis, X-ray powder diffraction, and IR and UV spectroscopy. A workflow for preparing potassium or ammonium amminetrichloroplatinate(II) from diamminedichloroplatinum(II) isomers was developed. This workflow appreciably increases the product yield due to the return of unused Magnus salt to the main synthesis flow.     

Kinetics and Mechanism of Reaction between N-Polyfluorophenylcarbonimidoyl Dichlorides and Tertiary Amines in Acetonitrile

The reaction of N-polyfluorophenylcarbonimidoyl dichlorides with tertiary amines in acetonitrile afforded chloroamidines R²NC(Cl) = NAr_F and alkyl chloride. The precursor of the products is the corresponding quaternary ammonium salt [R³N+C(Cl) = NAr_F]-Cl^-. The rate of the salt formation is described by a second order equation; however with some amines a saturation effect was observed for the reaction rate with the growing amine concentration. This fact and also the influence of the amine and the substrate structure on the reaction rate suggests that reaction proceeds by addition-elimination mechanism with formation of a tetrahedral intermediate. The latter in the rate-limiting stage undergoes a stereomutation into an intermediate of a configuration favorable for conversion into a quaternary salt.     

Angiotensin I retention behavior on Butyl-Sepharose under linear loading chromatographic conditions

Adsorption behavior of angiotensin I on a commercial Butyl-Sepharose support has been studied in function of temperature and ammonium sulphate concentration. Under isocratic elution conditions and at the higher salt concentrations, a characteristic of the chromatographic performance of angiotensin I was the broadness of the corresponding peak and in most of the cases the appearance of two peaks. These results have been interpreted in terms of on-column cis–trans isomerization of angiotensin I (a proline containing polypeptide) followed by its “re-conformation” after the interaction with the support. It has been proposed that the peak splitting phenomenon, a combined effect between temperature, salt concentration in the mobile phase and the ligand, is caused by slow kinetics of isomerization that is on the same time scale as the chromatographic separation. Salt concentration and temperature promote the conversion of the trans form of angiotensin I into its cis form, which has a bigger hydrophobic surface area, in the presence of Butyl-Sepharose. The retention of the cis form of angiotensin I increases with the increase in salt concentration in the mobile phase and seems to be little affected by temperature.     

Development of a spectrophotometric Sequential Injection Analysis (SIA) procedure for determination of ammonium: A Response Surface Methodology (RSM) approach

This paper describes the optimization and use of a Sequential Injection Analysis (SIA) procedure for ammonium determination in waters. Response Surface Methodology (RSM) was used as a tool for optimization of a procedure based on the modified Berthelot reaction. The SIA system was designed to (i) prepare the reaction media by injecting an air-segmented zone containing the reagents in a mixing chamber, (ii) to aspirate the mixture back to the holding coil after homogenization, (iii) drive it to a thermostated reaction coil, where the flow is stopped for a previously established time, and (iv) to pump the mixture toward the detector flow cell for the spectrophotometric measurements. Using a 100 μmol L^− 1 ammonium solution, the following factors were considered for optimization: reaction temperature (25 - 45 °C), reaction time (30 - 90 s), hypochlorite concentration (20 - 40 mmol L^− 1), nitroprusside concentration (10 - 40 mmol L^− 1) and salicylate concentration (0.1 - 0.3 mol L^− 1). The proposed system fed the statistical program with absorbance data for fast construction of response surface plots. After optimization of the method, figures of merit were evaluated, as well as the ammonium concentration in some water samples. No evidence of statistical difference was observed in the results obtained by the proposed method in comparison to those obtained by a reference method based on the phenol reaction.     

Prediction of the isothermal behaviour of solid-gas systems from non-isothermal data

A new procedure for the prediction of the isothermal behaviour of the solid-gas system from non-isothermal data is suggested. It bypasses the use of various approximations of the temperature integral that ground the integral methods of prediction. The procedure was checked for: (1) simulated data corresponding to a first order reaction; (2) experimental data obtained in the isothermal and non-isothermal decompositions of ammonium perchlorate. For the simulated data, a very good agreement between calculated isotherms and those evaluated by means of the suggested procedure was obtained. A satisfactory agreement (errors in time evaluation corresponding to a given degradation lower than 18%, for 0.10￡a￡0.37 and lower than 10% for 0.37￡a￡0.70) was obtained for the experimental data corresponding to the decomposition of ammonium perchlorate. In this last case, the mentioned differences between experimental and calculated data can be due both to the inherent errors in the evaluation of the decomposition isotherms and to the dependence of the activation energy on the conversion degree. This revised version was published online in July 2006 with corrections to the Cover Date.     

A novel four-component tandem protocol for the stereoselective synthesis of highly functionalised thiazoles

The reaction of bis(aroylmethyl) sulfides with aromatic aldehydes and ammonium acetate in 1:2:1 molar ratio under solvent-free microwave irradiation afforded predominantly a series of thiazoles, viz., 1-aryl-2-[5(Z)-5-arylmethylidene-2,4-diaryl-2,5-dihydrothiazol-2-yl]ethanones stereoselectively. This reaction presumably occurs via a Knoevenagel condensation-Michael addition-cyclocondensation-ring opening-ring closing Michael addition sequence. The intermediacy of (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) in the above transformation is demonstrated by their conversion to the thiazoles upon reaction with ammonium acetate under solvent-free microwave irradiation.     

Radioluminescence of Dy3+ in uranium-containing solutions of phosphorous oxychloride

Samples of POCl₃-SnCl₄-²³⁵UO₂-Dy³⁺ solutions have been prepared to investigate conversion of energy of heavy charged particles into optical radiation. Experimental data on radioluminescent characteristics of Dy³⁺ upon homogenous excitation of solutions by uranium α-radiation have been obtained. The efficiency of conversion of the energy of uranium α-particles into light energy depends on the Dy³⁺ concentration and the Dy³⁺ luminescence lifetime τ. At [Dy³⁺] = 0.2 mol/L and τ = 550 μs, the conversion efficiency is 0.12 ± 0.01% for the luminescent transition 4F ₉/2 → 6H ₁₃/2 (λ_max = 574 nm) or 0.20 ± 0.01% for the visible and near IR regions of Dy³⁺ luminescence.     

Statistical analysis of the influence of synthesis conditions on the properties of hierarchical zeolite Y

Commercial zeolite USY (CBV500, Si/Al = 2.6) was dealuminated with oxalic acid, desilicated with ammonium hydroxide assisted by cetyltrimethylammonium bromide, and acid washed with lactic acid for obtaining hierarchical zeolite Y. The samples were characterized by X-ray diffraction, N₂-physisorption, temperature programmed desorption of NH₃, transmission electronic microscopy and diffuse reflectance infrared Fourier transform spectroscopy Ppyridine adsorption. A central composite experimental design was used for obtaining the influence of the concentration of the three solutions used in each step of the synthesis, on the relative crystallinity (%RC), mesopore volume (V_meso), and total acidity of the synthesized materials. All the materials conserved the %RC and total acidity between 51-89% and 51–80%, respectively; modified materials showed an increase of up to 300 m²/g of external surface area and 0.17 cm³/g of the V_meso with respect to the CBV500 sample. The statistical analysis showed that all the properties are influenced by oxalic acid concentration, whereas ammonium hydroxide concentration affects V_meso, and lactic acid concentration affects %RC and total acidity in the modified samples. According to the optimization of the process, the material synthesized and labeled as MZ-OP, showed a %RC = 82%, V_meso = 0.21 cm³/g, and total acidity of 1.430 mmol/g. The catalytic cracking of n-dodecane was tested over CBV500, MZ-OP, and MZ-10-100-500 and the obtained conversion at 300 min was 65%, 95% and 82%, respectively. Deactivation rate of the modified samples was significantly lower than the values obtained with CBV500, showing that the modified samples were more stable under tested reaction conditions.     

Liquidus and glass transition temperatures of the ammonium nitrate-dimethylsulfoxide-water system

The liquidus temperature was measured in the ammonium nitrate-dimethylsulfoxide-water system over in the concentration range 0–60 mole% ammonium nitrate. The probable formation of the NH₄NO₃·nDMSO solvate with n=1.3–1.5 and the mixed solvate NH₄NO₃·DMSO·H₂O at 30 mole% ammonium nitrate and a DMSO:H₂O ratio of 4∶1 are indicated. The glass transition temperatures T _g were measured over a salt concentration range of 0–50 mol% ammonium nitrate and at various compositions of the mixed solvent (y _DMSO =0.1–0.9 mole fraction). At a constant mixed solvent composition, the dependence of the glass transition temperature on the salt concentration can be approximated by a linear relationship, as can its dependence on the DMSO content in the solution at constant salt concentration. The glass-forming composition regions were found and the limits of this region are discussed.     

High time resolution observation and statistical analysis of atmospheric light extinction properties and the chemical speciation of fine particulates

In recent years, the visibility deterioration caused by regional fine particulate pollution becomes one of the crucial air pollution problems in the urban areas of our country. The rapid variation of visibility and fine particulates make it difficult to estimate the relationship between them precisely and accurately unless high time resolution observation data can be accessed. This study aims to fill this gap in the field of atmospheric science by establishing a formula using multiple linear regressions. Excellent fitting goodness (R ² = 0.913, n = 3167) was obtained using 10 min average of high-resolution real-time light scattering coefficients, light absorption coefficients, main chemical speciation concentration in PM₁ and some meteorological parameters from 17 Jan to 16 Feb, 2009. It shows that the average light extinction coefficient during the observation in the winter of Shenzhen was measured to be 290 ± 183 Mm^?1, consisting of 72% of light scattering and 21% of absorption. In terms of the percentage contribution of PM₁ chemical species to the total light extinction, the organic matter was estimated to be most with an average of 45%, followed by ammonium sulfate with an average of 24%. The contributions of black carbon and ammonium nitrate were 17% and 12%, respectively. Besides, the diurnal variation of light extinction was investigated as well in this study.     

Axenic Cultures of Nitrosomonas europaea and Nitrobacter winogradskyi in Autotrophic Conditions: a New Protocol for Kinetic Studies

As a part of a natural biological N-cycle, nitrification is one of the steps included in the conception of artificial ecosystems designed for extraterrestrial life support systems (LSS) such as Micro-Ecological Life Support System Alternative (MELiSSA) project, which is the LSS project of the European Space Agency. Nitrification in aerobic environments is carried out by two groups of bacteria in a two-step process. The ammonia-oxidizing bacteria (Nitrosomonas europaea) realize the oxidation of ammonia to nitrite, and the nitrite-oxidizing bacteria (Nitrobacter winogradskyi), the oxidation of nitrite to nitrate. In both cases, the bacteria achieve these oxidations to obtain an energy and reductant source for their growth and maintenance. Furthermore, both groups also use CO₂ predominantly as their carbon source. They are typically found together in ecosystems, and consequently, nitrite accumulation is rare. Due to the necessity of modeling accurately conversion yields and transformation rates to achieve a complete modeling of MELiSSA, the present study focuses on the experimental determination of nitrogen to biomass conversion yields. Kinetic and mass balance studies for axenic cultures of Nitrosomonas europaea and Nitrobacter winogradskyi in autotrophic conditions are performed. The follow-up of these cultures is done using flow cytometry for assessing biomass concentrations and ionic chromatography for ammonium, nitrite, and nitrate concentrations. A linear correlation is observed between cell count and optical density (OD) measurement (within a 10?% accuracy) validating OD measurements for an on-line estimation of biomass quantity even at very low biomass concentrations. The conversion between cell count and biomass concentration has been determined: 7.1?×?10¹² cells g dry matter (DM)^?1 for Nitrobacter and 6.3?×?10¹² cells g DM^?1 for Nitrosomonas. Nitrogen substrates and products are assessed redundantly showing excellent agreement for mass balance purposes and conversion yields determination. Although the dominant phenomena are the oxidation of NH ₄ ⁺ into nitrite (0.95?mol?mol N^?1 for Nitrosomonas europaea within an accuracy of 3?%) and nitrite into nitrate (0.975?mol?mol N^?1 for Nitrobacter winogradskyi within an accuracy of 2?%), the Nitrosomonas europaea conversion yield is estimated to be 0.42?g DM mol?N^?1, and Nitrobacter winogradskyi conversion yield is estimated to be 0.27?g DM mol?N^?1. The growth rates of both strains appear to be dominated by the oxygen transfer into the experimental setups.     

Development and use of extraction sample preparation in the chromatographic-mass spectrometric studies of cognac products

The distribution of ethanol and butanol between n-hexane and aqueous solutions of ammonium sulfate at 20 ± 1°C was studied over an ideal concentration region of the substances in the organic phase. The distribution constants of the substances and the increments of the methylene and hydroxyl groups of the alcohols in the logarithm of the distribution constant were calculated. It was found that an increase in the salt concentration in the aqueous phase resulted in a considerable increase in the increment of the methylene group and significantly improved the alcohol separation efficiency. The dependence of the distribution coefficients of ethanol and butanol on the concentration of ethanol in the aqueous phase was studied. A dramatic decrease in the increment of the methylene group was found as the ethanol concentration in the salt phase was increased above 4.5 vol %. A procedure was developed for extraction sample preparation for the subsequent determination of the characteristic components of cognac products and for the authentication of these products by gas chromatography. The essence of this procedure consists in the hexane extraction of butanol and other hydrophobic substances from cognac product samples prediluted with an aqueous solution of ammonium sulfate. In this case, the major portion of ethanol, as well as hydrophilic and thermally unstable impurities, which complicate analysis with direct sample injection, remained in the salt solution. The procedure was tested with 16 samples of cognac and cognac spirits from Georgia, including both authentic and adulterated products.     

Hybrid sequential injection-flow injection manifold for the spectrophotometric determination of total sulfite in wines using o-phthalaldehyde and gas-diffusion

A new automated spectrophotometric method for the determination of total sulfite in white and red wines is reported. The assay is based on the reaction of o-phthalaldehyde (OPA) and ammonium chloride with the analyte in basic medium under SI conditions. Upon on-line alkalization with NaOH, a blue product is formed having an absorption maximum at 630 nm. The parameters affecting the reaction - temperature, pH, ionic strength, amount concentration and volume of OPA, amount concentration of ammonium chloride, flow rate and reaction coil length - and the gas-diffusion process - sample and HCl volumes, length of mixing coil, donor flow rate - were studied. The proposed method was validated in terms of linearity (1-40 mg L⁻¹, r = 0.9997), limit of detection (c_L = 0.3 mg L⁻¹) and quantitation (c_Q = 1.0 mg L⁻¹), precision (s_r = 2.2% at 20 mg L⁻¹ sulfite, n = 12) and selectivity. The applicability of the analytical procedure was evaluated by analyzing white and red wine samples, while the accuracy as expressed by recovery experiments ranged between 96% and 106%.     

Improved Protocol for Somatic Embryogenesis and Calcium Alginate Encapsulation in Anethum graveolens L.: A Medicinal Herb

An improved procedure has been developed for efficient somatic embryogenesis in Anethum graveolens. Green friable embryogenic callus was obtained from hypocotyl segments on medium augmented with 2,4-dichlorophenoxyacetic acid (2,4-D). The highest embryogenic callus induction frequency of 87 % was obtained on Murashige and Skoog (MS) medium containing 1.13 μM 2,4-D. At lower concentration of 2,4-D (0.34 μM) callus turned dark in color and slow growing. Embryogenic cultures (76 %) responded with a mean number of 43 globular and 18 heart stage embryos. Somatic embryo maturation and subsequent conversion into plantlets took place on MS lacking growth regulators. Maximum number of somatic embryos developed on MS medium was 128.3 (per flask) and a plantlet conversion of 82 % was observed. Calcium alginate beads were produced by encapsulating somatic embryos. Highest percent germination (83 %) was observed on 0.8 % agar solidified MS medium with the plantlets acquiring an average length of 2.1 cm. Encapsulated somatic embryos could be stored at 4 °C up to 60 days with a conversion frequency of 49.3 %. Highest protein and proline content has been observed in embryogenic callus with small globular embryos. During morphological differentiation of the somatic embryos, changes in the antioxidant enzymatic system were observed. Superoxide dismutase (SOD) activity increased during initial stages and decreased catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) activities were detected.     

Optimization of dynamic pH junction for the sensitive determination of amino acids in urine by capillary electrophoresis

A capillary electrophoresis method with UV-absorbance detection was studied and optimized for the determination of underivatized amino acids in urine. To improve concentration sensitivity the utility of in-capillary analyte stacking via dynamic pH junction was investigated with phenylalanine (Phe) and tyrosine (Tyr) as model amino acids. Before sample injection, a plug of ammonium hydroxide solution was injected to enable analyte concentration. Samples were 1:1 (v/v) mixed with background electrolyte (1 M formic acid) prior to injection. The effect of the injected sample volume, and the injected ammonium hydroxide volume and concentration on analyte stacking and separation performance was investigated. The optimal volume of ammonium hydroxide depended on the injected sample volume. Using a dynamic pH junction good resolution (1.4) was obtained for a sample injection volume of 10% of the capillary (196 nl) with Phe and Tyr dissolved in water. Limits of detection (LODs) were 0.036 and 0.049 μM for Phe and Tyr, respectively. For urine samples, the optimized procedure comprised a 1.7-nl injection of 12.5% ammonium hydroxide, followed by a 196-nl injection of urine spiked with Phe and Tyr. Satisfactory resolution was obtained and amino acid peak widths at half height were only 1.6 s indicating efficient stacking. Calibration plots for Phe and Tyr in urine showed good linearity (R(2) > 0.96) in the concentration range 10-175 μM, and LODs for Phe and Tyr were 0.054 and 0.019 μM, respectively. RSDs for peak area and migration time for Phe and Tyr were below 7.5% and 0.75%, respectively.