Thermodynamic and physical properties of carbon tetrachloride + sulfolane mixtures

The solid + liquid phase diagram, drawn from thermal and dielectric measurements, is presented. It exibits a miscibility gap at 0.08 ≤ χ₂ ≤ 0.58, and two eutectics. The occurrence of a (likely 1:1) intermediate compound, which decomposes on melting into two immiscible liquids, is postulated. Mixed crystals are observed in the sulfolane richer region.Deviations of the liquid mixtures from ideality, positive in the case of viscosity and negative in the case of dielectric constants, are evidenced.     

High-performance liquid chromatography – atmospheric pressure negative chemical ionisation – mass spectrometry of 2,4-dinitrophenyl derivatives of amines

High-performance liquid chromatography (HPLC) coupled to mass spectrometry (MS) is used to detect 2,4-dinitrophenyl (DNP) derivatives of amines by means of negative chemical ionisation at atmospheric pressure. The high sensitivity and good comparability of UV- and MS-detection of DNP-derivatives of amines is shown by several examples. The high selectivity of the derivatisation and the detection method (UV and MS) is used for the analysis of unknown amines in aqueous phases after hydrolytic degradation of polyamide-amine- or polyamine-epoxide-adducts as well as for the characterisation of commercial products.     

Rapid and sensitive determination of urinary 2,5-hexanedione by reversed-phase high-performance liquid chromatography.

A rapid and sensitive method for the determination of 2,5-hexanedione (HD) (the principal metabolite of n-hexane) in urine samples by reversed-phase high-performance liquid chromatography (HPLC) is described. The sample preparation procedure was based on solid-liquid extraction after acid hydrolysis; it was optimized to enable accurate HD determination in less than 30 min. Analysis of spiked real samples showed a recovery of more than 85% at the 0.1-ppm level, with a relative standard deviation of 5% and a detection limit as low as 0.01 ppm. Intra-assay and inter-assay coefficients of variation at the 0.5-ppm level were 4 and 5%, respectively. The chromatographic peak assigned to HD was identified by collecting the HPLC eluate at the retention time of HD and analysing it using Fourier transform infrared spectrometry coupled with high-resolution gas chromatography. Urine samples of unexposed and exposed subjects were analysed following the proposed analytical procedure. HPLC and high-resolution gas chromatographic analyses were also compared on these samples. A correlation factor of 0.992 was obtained, which showed a good agreement between the two sets of data.     

Computer simulation studies of anisotropic systems. The influence of external fields on the nematic—isotropic transition

The results of Monte Carlo simulations are reported for a model nematogen in the presence of an intense magnetic field. The predictions of a molecular field theory for the system are found to be in reasonable accord with the simulations. It would appear therefore that the critical field for a real nematogen may be unobservably high.     

Organotellurium derivatives of dicarboxylic acids

The freshly prepared sodium salts of ortho-phthalic acid and tetrabromo ortho-phthalic acid react with diaryltellurium dichlorides in chloroform to afford new dimeric organotellurium carboxylates, R₂Te(C₈X₄O₄)₂ (X = H, Br). The new compounds contain fourteen membered rings and the detailed structure is discussed particularly in the light of the ¹H NMR spectrum of (p-EtOC₆H₄)₂Te(C₈H₄O₄)₂ which shows inequivalence of p-ethoxy groups. The sebacate derivatives of tellurium(IV) are oligomeric and iso- and terephthalic acids failed to give well defined products.     

Zur Diels-Alder-Reaktion der Dihydro-6-styryl-2(1H)-pyrimidinone

Dihydro-6-styryl-2(1H)-pyrimidinones react with dienophiles such as maleic anhydride in form of aDiels—Alder reaction.     

Direct analysis of selected N-acyl-L-homoserine lactones by gas chromatography/mass spectrometry

A rapid, simple and selective method involving direct separation by gas chromatography (GC) with electron ionization mass spectrometry (EI-MS) was employed to determine some N-acylhomoserine lactones (AHLs). Using GC/EI-MS, simultaneous separation and characterization of AHLs were possible without prior derivatization. Informative fragmentation patterns were obtained to identify the structures of N-acyl chains of AHLs. Electron ionization resulted in a common fragmentation pattern with the most abundant ion at m/z 143 and other minor peaks at m/z 71, 57, and 43. The presence of AHLs in extracts of Burkholderia cepacia strains was achieved in selected ion monitoring mode by using the prominent fragment at m/z 143.     

Solid-supported Hantzsch—Biginelli reaction for syntheses of pyrimidine derivatives

The microwave-assisted dry media technology was utilized for the synthesis of some novel derivatives in the Hantzsch—Biginelli reaction. In this eco-friendly approach, the usage of organic solvents and hazardous reagents resulting in corrossion of materials was minimized, giving high yields of products within a short reaction time.     

Radiometrische schnellbestimmungen mit ädte durch rückmessung

The principle of back-titration with EDTA is applied to rapid radiometric methods. A suitable vessel for performing the reaction, filtration and count-rate measurement is described. The optimal conditions for the use of solid ^110mAgIO₃ as indicator were studied: the time for solubility-equilibrium of solid silver iodate, the reaction time of EDTA with silver iodate, and the pH-dependence of the silver-EDTA reaction rate. Procedures are given for calibration curves and for rapid radiometric determinations of copper(II). nickel(II), lead(II) and zinc(II). The method is suitable for the range 1–100μg.