A gas chromatographic-mass spectrometric method for trace analysis of chlorofluorocarbons and their replacement compounds in atmospheric samples

Summary The simultaneous determination of chlorofluorocarbons and their replacement compounds in ambient air samples requires the preconcentration of appropriate air volumes on suitable adsorbents. The performance of a dual-layer adsorption tube to be used in this type of analysis was evaluated in terms of breakthrough volumes (BTV) for the compounds of interest at ambient temperature. To verify the effectiveness of such adsorption tubes, real air samples were enriched at ambient temperature and were subsequently analyzed by capillary gas chromatography coupled with quadrupole mass spectrometry, operating in SIM mode. The results obtained confirmed the efficacy of the proposed method, in terms both of sensitivity and chromatographic separation efficiency.     

Aluminium fractionation using cation exchange: comparison of results obtained after fractionation in the field and in the laboratory

Dissolved aluminium was fractionated in the field and the laboratory using a cation-exchange method. Although absolute differences between results obtained from field and laboratory fractionations were generally small, relative differences, expressed as the ratio between labile aluminium determined after laboratory fractionation (Al_ll) and that obtained after field fractionation (Al_lf) could be large. The differences found were not statistically significant, although this may simply reflect the spread in the results. Al_ll/Al_lf had no apparent relationship with the temperature difference between the field and the lab. Although some significant correlations were found between Al_ll/Al_lf and H⁺, no significant correlations were found with the equivalent relative difference in {H⁺} between the lab and the field; nor was any significant correlation found with dissolved organic carbon.     

Voltammetry at the mercury film electrodes: Comparison of theoretical and experimental results obtained for indium in thiocyanate medium

The voltammetric behaviour of the In(III)-In(Hg) system was studied at the silver-, graphite-, and glassy carbon-based mercury film electrodes under cyclic and stripping conditions in thiocyanate media. The reversible curves obtained at high thiocyanate ion concentration showed a good agreement with theoretical predictions, particularly for the cathodic process. The anodic curves obtained at thin silver-based mercury film electrodes deviated from theoretical predictions due to the interactions between indium, dissolved in mercury, and the silver substrate of the film electrode. At low thiocyanate ion concentrations, where the current was controlled partly by the rate of the preceding chemical step and partly by diffusion, the variations in the film thickness affected the position of the curve as predicted theoretically for the reversible diffusion controlled case.     

Density of methanol-carbon dioxide mixtures at three temperatures: Comparison with vapor-liquid equilibria measurements and results obtained from chromatography

The density of methanol-carbon dioxide mixtures has been measured at 40, 50, and 60°C and the data presented as constant density curves in plots of pressure against composition. Mixtures containing from 1 to 23.5% methanol were covered. The density information was compared with liquid-vapor equilibria data from the literature and with results from chromatographic separations using both sub- and supercritical conditions. The results indicate that phase transitions do not usually occur when the concentration of the modifier is increased while holding temperature and pressure constant. Similarly, no phase transition occurs when the temperature is increased from 28 to 80°C, at a constant (high) pressure and modifier concentration. Binary fluids with many desirable compositions cannot be prepared at low densities: densities below 0.4–0.5 g/cm³ cannot be obtained from methanol-carbon dioxide mixtures because the fluids separate into two phases. This means that density programming with many binary fluid combinations will be of secondary importance compared with composition programming.     

Improved radioxenon gamma-spectrometry counting system and its efficiency calibration: Monte Carlo simulation and experimental results at enriched xenon counting environment

To give satisfactory efficiency both for X- and gamma-ray photon, an improved counting system has been developed in CTBT Canadian radioxenon laboratory. The counting system consists of a BEGe detector coupled with a thin carbon fiber window counting cell, that can perform a reliable and efficient radioxenon measurement. A semi-empirical calibration procedure was adopted, which is a combination of experimental measurement and mathematical simulation. Mathematical calibration tool is Monte Carlo simulation software named VGSL. Advanced gamma-spectrum analysis software, named Aatami, was used for gamma-ray peak shape fitting and X-ray multiplets deconvolution. The calculated full energy peak efficiency curve covers from 30 to 700 keV and agrees well with experimental data points within 2%. The efficiency curve can provide radioxenon analysis both for X-rays and gamma-rays with high quality. The efficiency distortion near xenon k-absorption edge of 35 keV, which is caused by high concentrated xenon in the counting cell, is also discussed.     

Molecular polarizability of organic compounds and their complexes: LI. Molar volumes and steric structure of intracomplex compounds in solutions at infinite dilution

Molar volumes in solutions at infinite dilution were determined for a series of intracomplex compounds of beryllium, zinc, cobalt, copper, and nickel, derived from salicyalalanilines, salicylalalkylimines, N-[(2-hydroxyphenyl)(methyl)methylene]anilines, N-[(2-hydroxyphenyl)(phenyl)methylene]aniline, as well as ethylene glycol and glycerol. An additivity scheme was constructed for calculation of the molar volumes of these compounds in solutions. Analysis of the experimental molar volumes of the systems studied showed that chelation via intramolecular complex formation almost always makes these values lower than those calculated by the additivity scheme, implying entropy stabilization of the chelates in solutions due to release of solvent molecules from the solvation shell of the molecules. It was shown that the dipole moments and Kerr constants of those compounds for which the additive scheme for calculation of molar volumes was constructed can be much easier estimated.     

Determination of organic and inorganic mercury compounds by reverse-phase high-performance liquid chromatography after extraction of the compounds as their dithizonates

A sensitive and selective method is described for the simultaneous determination of inorganic and organic mercury compounds. The mercury compounds are extracted into toluene or chloroform with dithizone, and the dithizonates are separated by liquid chromatography on an ODS column. Complete resolution was obtained between methylethyl-, phenyl- and inorganic mercury with a mobile phase of THF/methanol (2:1) with 0.05 M acetate buffer pH 4 (62 + 38), containing 50 μM EDTA. The mercury chelates were detected spectrophotometrically at 475 nm. The detection limits were at the subnanogram level. The method is applicable to human urine, tap water and tomatoes.     

Hydration of DNA-binding biological active compounds: EHF dielectrometry and molecular modeling results

We report hydration properties of several DNA-binding ligands (pharmaceutical drug caffeine; mutagens proflavine, ethidium bromide, propidium iodide; polyamines putrescine, spermine), which are able to interact with DNA in different modes via external binding, intercalation or minor groove binding. We show that the detection of the bound water molecules and the estimation of their amount in aqueous solutions of ligands can be efficiently carried out using the measurements of complex dielectric permittivity of the solutions in the millimeter range of radio waves. Our dielectrometric data are combined with the results of the molecular modeling including quantum chemical calculations and Monte Carlo simulations. We show that number of water molecules able to form hydrogen bonds with donor–acceptor groups of ligands correlates with hydration numbers taken from the literature or obtained in EHF dielectrometry experiment. The latter indicates that the EHF dielectrometry method is sensitive for the tightly bound water molecules.     

Heavy alkali metal-arsenic alloy-based graphite intercalation compounds: Investigation of their synthesis and of their physical properties

Heavy alkali metal-arsenic alloys intercalate easily into graphite, leading to the formation of a new family of ternary graphite intercalation compounds (GICs). Pure phases formulated as MAsxC4s (M = K, Rb or Cs; s = stage; x ≤ 1) have been synthesized at the laboratory. This article aims to expose all physical measurements performed on these intercalation compounds to get an idea about their electronic properties.Electrical conductivity measurements have been performed both parallel and perpendicular to the basal planes, between 4.2 and 295 K. Room temperature resistivity values lie between 16 and 35 μΩ cm and the anisotropic resistivity takes a value of an order of magnitude of 10⁴. Dynamic magnetic susceptibility measurements, carried out at low temperature on some phases, showed that they do not exhibit superconducting transition up to 1.3 K. Raman spectroscopy investigation, which is a useful tool to study the electronic and the chemical stability of GICs, highlighted a significant up-shift of the G-band of the carbon intra-layer vibration frequency, compared to the pure graphite vibration mode. Undoubtedly, this is related to the electronic charge transfer established between graphite layers and intercalated species.     

Blood lead monitoring in Italy: Assessment of the quality of results obtained between 1992 and 1994

Between 1992 and 1994, a new screening campaign for blood Pb monitoring in the Italian general population was carried out. Since the first campaign (started in 1978, in accomplishment of the European Community Directive 77/312/EEC) a working group of the Laboratory of Clinical Biochemistry at the Italian National Institute of Health (Istituto Superiore di Sanità), as the Reference Centre (RC), has coordinated the activity of various laboratories spread over the national territory. Appropriate quality assurance procedures, including an external quality assessment scheme (EQAS), were elaborated. Within the EQAS, three or four trials were carried out every year. Each laboratory participating in the trial analyzed eight control samples prepared from cow blood at different Pb concentrations. The results obtained by each peripheral laboratory and the RC between 1992 and 1994 have been compared by regression analysis. The same statistical method was adopted to compare the results obtained by each peripheral laboratory and the RC in the duplicate analysis of about 10 per cent of the human samples collected during the 1992–1994 monitoring campaign. There was no evidence of systematic differences between the regression lines obtained on control and human samples. In spite of the lower Pb concentration in the control samples analyzed during the 1992–1994 campaign, the analytical performance of the laboratories was better than that obtained in the previous screening campaign (1985–1986). Blood Pb levels observed in human samples collected between 1992 and 1994, confirm the downward time trend observed in the campaigns carried out in 1978–1979, 1980–1981 and 1985–1986. This study confirms that the results obtained in an EQAS are representative of the actual performance in the analysis of real (human) samples.     

Studies on pyrazine derivatives LII: Antibacterial and antifungal activity of nitrogen heterocyclic compounds obtained by pyrazinamidrazone usage

Using reactivity of pyrazinamidrazones and their N′‐substituted derivatives 1–8 in reaction with sulfonyl chlorides sulfone derivatives 9–17 were obtained, with orthoformate cyclized to sulfonyl compounds 18–20 . Amidrazones in reaction with pyraziniminoesters gave dihydrazidines 21–23 , which cyclized to 3,5‐dipyrazine derivatives of 1,2,4‐triazole 24–26 . 1‐Methyl‐ or 1‐phenyl‐3‐pyrazine‐1,2,4‐triazole 27–38 was formed in reaction of amidrazones 1–8 with orthoformate and orthoacetate or benzoyl chloride. N′‐Phenylamidrazones 3, 8 in reaction with thionyl chloride were transformed to 1,2,3,5‐thiatriazole S‐oxides 39, 40 . Obtained compounds exhibited low antibacterial activity. Antifungal activity was affirmed for compounds 1, 3, 4, 5, 8, 37, 39, and 40 , for which minimal inhibitory concentration (MIC) was in the concentration range of 16–128 μg/mL. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 23:49–58, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20751     

Perfluoroalkanesulfonylimides and their lithium salts: synthesis and characterisation of intermediates and target compounds

ECF processes have been extensively experienced and developed since early 1970s at the Fluorine Chemistry Laboratory of Padua University: several classes of perfluorinated inert and functional compounds have been obtained, in particular perfluoro heterocyclics and perfluorinated acid fluorides.Recently the demand for electrolyte salts, applied in lithium batteries, drove our interest to investigate on the perfluoroalkanesulfonylimides.A series of the perfluoroalkanesulfonylfluoride precursors has been obtained by ECF and their metathesis to the related imides and lithium salts has been investigated.A number of representative products has been obtained and characterized in their structure and ionic conductivity.     

Biopolyols obtained via crude glycerol-based liquefaction of cellulose: their structural,rheological and thermal characterization

In this work lignocellulose biomass liquefaction was used to produce biopolyols suitable for the manufacturing of rigid polyurethane foams. In order to better evaluate the mechanism of the process, pure cellulose was applied as a raw material. The effect of time and temperature on the effectiveness of liquefaction and the parameters of resulting biopolyols were characterized. The prepared materials were analyzed in terms of their chemical structure, rheology, thermal and oxidative stability, and basic physical and mechanical properties that are important from the point of view of polyurethane manufacturing. The optimal parameters for the biopolyol production with a 94 % yield were achieved at 150 °C for a 6-h reaction duration. The obtained polyols were characterized by the hydroxyl number of 643 mg KOH/g and enhanced thermal and oxidative stability compared to the polyols obtained at lower temperatures, which is associated with the altered mechanism of liquefaction. The results of rheological tests, analyzed with the use of Ostwald-de Waele and Herschel Bulkley models, revealed that the prepared biopolyols can be classified as pseudoplastic fluids with the viscosity values similar to those of commercially available products. Rigid foams obtained via partial substitution of petrochemical polyol with prepared bio-based one were characterized by slightly increased apparent density and average cell size comparing to unmodified materials. The best mechanical performance was observed for the sample containing 35 wt% of biopolyol in the polyol mixture, which indicates a synergistic effect between the applied polyols. The applied modification delayed thermal degradation of foams due to changes in thermal decomposition process. In conclusion, the presented work confirms that lignocellulose biomass liquefaction can be successfully applied as a manufacturing method of polyols later used in the production of polyurethanes.     

Adducts of coordination compounds—12: New hydrogen dinitrates and their structures

The new compounds trans-[Ru(pyr)₄Cl₂[H(ONO₂)₂] and [C₁₃H₉NH][H(ONO₂)₂] have been characterised (where pyr is pyridi     

Halodiazirines and halodiazo compounds: a computational study of their thermochemistry and isomerization reaction

A computational study of the isomerization reaction of a series of halodiazirines to halodiazo compounds (cyclic to open-chain RXCN₂ species) has been carried out in order to establish the effect of the substituent groups on the isomerization rates and to obtain computational evidence of reaction mechanisms. Fluorine and chlorine were present as the halogen (X) atom, and the groups R=H, CH₃, C₂H₅, n-C₃H₇, i-C₃H₇, cyclo-C₃H₅, phenyl, OCH₃ and OH were used. Thermochemical calculations and natural bond orbital analyses were carried out at the B3LYP/6-31+G(d,p) level of theory. The results allowed us to discuss a reaction mechanism that proceeds in two steps: The first is the extrusion of nitrogen and formation of a carbene through a cyclic transition state that promotes the simultaneous breaking of the two C–N bonds, and the second one is described as the rebounding between the carbene and one of the nitrogen atoms of molecular nitrogen, both formed in the first step. The enthalpies of formation of halodiazirines and halodiazoalkanes have been calculated at the G3 level of theory.     

Static and dynamic properties of tethered chains at adsorbing surfaces: a Monte Carlo study

We present extensive Monte Carlo simulations of tethered chains of length N on adsorbing surfaces, considering the dilute case in good solvents, and analyze our results using scaling arguments. We focus on the mean number M of chain contacts with the adsorbing wall, on the chain's extension (the radius of gyration) perpendicular and parallel to the adsorbing surface, on the probability distribution of the free end and on the density profile for all monomers. At the critical adsorption strength epsilon(c) one has M(c) approximately N(phi), and we find (using the above results) as best candidate phi to equal 0.59. However, slight changes in the estimation of epsilon(c) lead to large deviations in the resulting phi; this might be a possible reason for the difference in the phi values reported in the literature. We also investigate the dynamical scaling behavior at epsilon(c), by focusing on the end-to-end correlation function and on the correlation function of monomers adsorbed at the wall. We find that at epsilon(c) the dynamic scaling exponent a (which describes the relaxation time of the chain as a function of N) is the same as that of free chains. Furthermore, we find that for tethered chains the modes perpendicular to the surface relax quicker than those parallel to it, which may be seen as a splitting in the relaxation spectrum.     

Structure of ABCA tetrablock copolymer vesicles and their formation in selective solvents: a Monte Carlo study

Vesicles formed by ABCA tetrablock copolymers in solvents that are selective for block A are studied using the Monte Carlo simulation. Simulation results show that the chain length ratio and hydrophobicity of blocks B and C are key factors determining the hydrophobic layer structure of the vesicles. If the B and C blocks are of the same hydrophobicity, the longer block C tends to form the closed hydrophobic layer, whereas the shorter block B is located on the outer surface of the closed hydrophobic layer. However, if the hydrophobicity difference between blocks B and C is high enough, the reverse will occur given that block B has a higher hydrophobicity and block C has a lower hydrophobicity. The kinetics of vesicle formation is also studied. Simulation results reveal that the hydrophobic layer structure is formed through the migration of the polymer chain within the vesicle membrane after the formation of the vesicle profile. This migration is independent of the differences in chain length ratio and the hydrophobicity between the blocks B and C. The packing mode and the migration of polymer chains within the vesicle membrane are also presented and discussed.