A novel equation of state for the prediction of thermodynamic properties of fluids

This work proposes a new equation of state (EOS) based on molecular theory for the prediction of thermodynamic properties of real fluids. The new EOS uses a novel repulsive term, which gives the correct hard sphere close packed limit and yields accurate values for hard sphere and hard chain virial coefficients. The pressure obtained from this repulsive term is corrected by a combination of van der Waals and Dieterici potentials. No empirical temperature functionality of the parameters has been introduced at this stage. The novel EOS predicts the experimental volumetric data of different compounds and their mixtures better than the successful EOS of Peng and Robinson. The prediction of vapor pressures is only slightly less accurate than the results obtained with the Peng-Robinson equation that is designed for these purposes. The theoretically based parameters of the new EOS make its predictions more reliable than those obtained from purely empirical forms.     

Spectrophotometric determination of copper(II), nickel(II) and cobalt(II) as complexes with sodium diethyldithiocarbamate in cationic micellar medium of hexadecyltrimethylammonium salts

The determination of copper(II), nickel(II) and cobalt(II) was carried out as diethyldithiocarbamate (DDTC) complexes in presence of aqueous solutions of cationic surfactants of hexadecyltrimethylammonium bromide, chloride and hydroxide (CTAB, CTAC, CTAOH). The presence of micellar systems avoids the previous step of solvent extraction necessary to the formation of the DDTC complexes in absence of micelles. The influence of the different micellar counterions on the analytical characteristics (sensitivity and detection limits) of the proposed method for spectrophotometric determination of Cu(II), Ni(II) and Co(II) was studied.     

Preparation and Characterization of Cu(II) Phthalocyanine Tetrasulfonate Intercalated and Supported on Layered Double Hydroxides

The aim of the present work was to synthesize and characterize layered doublehydroxides (LDHs), in the magnesium/aluminum form, intercalated with copper(II)phthalocyanine tetrasulfonate (CuPcTs). The metal complex was immobilized intothe LDH gallery region through the reconstitution method and this material wascharacterized by X-ray diffraction (XRD), surface area and porosity measurements,elementary analysis, thermogravimetry (TGA), vibrational (IR) and electronic(UV-visible) spectroscopies, and electronic paramagnetic resonance (EPR). Thecatalytic performance of CuPcTs intercalated and supported on the LDH wasevaluated by carrying out the hydrogen peroxide dismutation. The CuPcTs wassuccessfully intercalated into the LDH layers according to XRD data (the basalspacing of the carbonate precursors increases by approximately 15Å inthe intercalated samples). The surface area and porosity analysis suggested thatthe CuPcTs intercalated materials are not microporous solids. Samples containingthe metal complex confined between the LDH layers have an appreciable thermalstability: decomposition is not observed at least up to 400 °C. TGA experiments also show that the weight-loss curves of the CuPcTs supported samples superimpose those recorded for the CuPcTs complex and the LDH-carbonate while the curves for theintercalated materials are unique. CuPcTs intercalated or supported on LDHs is notactive in the hydrogen peroxide dismutation although the free form shows activity at pH above 8.     

Calculation of hfs coupling constants by the roothaan “Plus” configuration interaction method within the INDO approximation

A new set of parameters, relating hfs coupling constants to the spin densities calculated by the RHF+CI method, within the INDO approximation, is given for¹H, ¹³C, ¹⁴N, ¹⁷O, ¹⁹F. On the whole the results, obtained for a homogeneous sample of organic radicals, are in better agreement with experimental ones, as compared with UHF method.     

An Improved Phenylselenoetherification of Pent-4-en-1-ol

The procedure employs phenylselenyl chloride or bromide, pent-4-en-1-ol, and additives, like pyridine and silver(I) salts, to generate the cyclic ether of tetrahydrofuran type in high yields. A catalytic amount of additive leads to higher yields, but equimolar amounts achieved almost quantitative yields under extremely mild experimental conditions. The effect of the halide ion of the selenylating reagent is not significant.     

Activity of MoSe2/Al2O3 catalysts in decomposition of thiophene and selenophene

The rate of thiophene decomposition was shown to be independent of the type of chalcogens used in catalysts MoX₂/Al₂O₃, where X = S, Se. On the contrary, the rate of selenophene decomposition was shown to be higher on catalysts MoSe₂ than that on MoS₂. This observation suggests that the decomposition proceeds on anion vacancies. The decomposition of either thiophene over MoSe₂ or selenophene over MoS₂ results in the formation of partially substituted chalcogenides. At that, the molar ratios of the substituted chalcogen to Mo were shown to coincide in both cases. The fact that the rate of the thiophene decomposition does not depend on the degree of anion exchange indicates that the decomposition is not associated with hydrogenolysis.     

Separation of metal complexes by on-line coupled LC-GC

The on-line coupled LC-GC technique was applied to the analysis of several metal chelates of N,N-diethyldithiocarbamic acid. A 10-port valve interface was used to couple the LC and GC instruments. Conditions during sample transfer into the GC gave fully concurrent solvent evaporation. The chelates investigated were separated with a short apolar fused silica column. LC preseparation was made with cyano or amino phases using a hexane/dichloromethane mixture as eluent. On-line LC-GC combination seems to be very suitable for the separation of the metal chelates studied.     

Detection of sugar addition to citrus juices by capillary GC

A method is described for the detection of citrus juices adulterated by addition of industrial sugar products. The oligosaccharides maltotriose (DP3) and maltotetraose (DP4), both of which are absent from the natural sugar profile of citrus fruits, serve as markers. The sample preparation method includes clean-up on a solid phase ODS cartridge, fractionation of DP3 and DP4 carbohydrates by LC on aminopropyl silica gel, and derivatization of the collected sugars to form the oxime-trimethylsilyl derivatives. Capillary GC analysis is performed on a 30 m × 0.32 mm i.d. polydimethylsiloxane fused silica column applying cool on-column injection and FID detection. The detection limit for maltotriose and maltotetraose is about 1 mg l^?1. Several orange and grapefruit juices were evaluated on their authenticity. Adulteration with crystalline sugar products cannot be detected with the described procedure.     

Enantioselective analysis of ibuprofen in human plasma by anionic cyclodextrin-modified electrokinetic chromatography

This paper reports the development of a rapid method for the enantioselective analysis of the nonsteroidal anti-inflammatory drug ibuprofen in human plasma by capillary electrophoresis employing the anionic cyclodextrin-modified electrokinetic chromatography mode. Sample cleanup was carried out by acidification with HCl followed by liquid-liquid extraction with hexane:isopropanol (99:1 v/v). The complete enantioselective analysis was performed within 10 min, using 100 mmol L(-1) phosphoric acid/triethanolamine buffer, pH 2.6, containing 2.0% w/v sulfated beta-cyclodextrin as chiral selector; fenoprofen, another nonsteroidal anti-inflammatory drug, was used as internal standard. The calibration curves were linear over the concentration range of 0.25-125.0 microg mL(-1) for each enantiomer of ibuprofen. The mean recoveries for ibuprofen enantiomers were up to 85%. The enantiomers studied could be quantified at three different concentrations (0.5, 5.0 and 50.0 microg mL(-1)) with a coefficient of variation and relative error not higher than 15%. The quantitation limit was 0.2 microg mL(-1) for (+)-(S)- and (-)-(R)-ibuprofen using 1 mL of human plasma. The plasma endogenous compounds and other drugs did not interfere with the present assay. The analysis of real plasma samples obtained from a healthy volunteer after administration of 600 mg of racemic ibuprofen showed a maximum plasma level of 29.6 and 39.9 microg mL(-1) of (-)-(R)- and (+)-(S)-ibuprofen, respectively, and the area under plasma concentration-time curve AUC(0-infinity) (+)-(S)/AUC(0-infinity) (-)-(R) ratio was 1.87.     

Capillary electrophoretic analysis of inorganic anions in atmospheric hailstone samples

Micellar electrokinetic capillary chromatography (MEKC) coupled with sample stacking and polarity switching was investigated for the determination of Viagra (sildenafil citrate, SC) and its metabolite (UK-103,320, UK) in human serum in the concentration range of clinical interest. Human serum samples spiked with SC and UK were eluted with methanol from a C18 cartridge, the extract was evaporated and regenerated in a solution that contained 1 mM phosphate buffer (pH 12.3) and 20% methanol. The MEKC separation was performed using an injection time of 275 s, a polarity switching time of 93 s, a phosphate buffer, (pH 12.3, 15 mM) containing 25 mM sodium dodecyl sulfate as separation electrolyte and a fused-silica capillary. The analysis takes about 6 min and gives satisfactory inter-day precision with respect to migration times and linear responses over the 80-900 ng/ml concentration range investigated for SC and UK. Intra-day RSDs (n=4 graphs) for the slopes of the calibration graphs were 4.86% for SC and 3.50% for UK. Inter-day RSDs for the slopes were 4.37% for SC and 5.39% for UK. Detection limits (S/N=3) were about 17 ng/ml for both compounds in human serum. A 1-ml volume of blood serum was necessary to do this determination.