Limiting Partial Molar Volumes of Electrolytes in 2-Methyl-2-Butanol <Emphasis Type="Bold">+</Emphasis> Water Mixtures at 298.15 K

Partial molar volumes at infinite dilution, V⁰₂, of alkali–metal halides (LiCl, NaCl KCl RbCl CsCl, NaBr, KBr, KI), tetra-n-alkylammonium bromides, R₄NBr (R=Me, Et, n-Pr, n-Bu, n-Pen), NaBPh₄, and Ph₄PCl have been determined in binary solvent mixtures of water with 2-methyl-2-butanol covering the water-rich region and the alcohol-rich region at 298.15 K. V⁰₂ for alkali–metal halides show relatively little dependence on the solvent composition. However, in the case of hydrophobic electrolytes the observed effects are more pronounced. A good linear dependence between V⁰₂(R₄NBr) and the molecular weight of the tetra-n-alkylammonium cation is found. Limiting single-ion volumes have been obtained using the assumption that V⁰(Ph₄P⁺)–V⁰(BPh^–₄)=2.0 cm³-mol^–1. The trends in the single-ion volumes are discussed in both solvent regions.     

Unprecedented eight-palladium(I) crown-cycle with metal-metal unsupported bonds

Tri(N-pyrrolyl)phosphine reacted with the sigma/pi complex [Pd(mu-Cl)(COD-MeO)]2 to give the octa-cycle [Pd(mu-Cl)[P(pyrl)3]]8 containing four Pd(I)-Pd(I) unbridged bonds.     

Liquid chromatography with ultraviolet absorbance detection for the analysis of tetracycline residues in honey

The separation of tetracyclines (TCs) using reversed-phase liquid chromatography (LC) is proposed. The use of an amide-based stationary phase prevents the interaction of tetracyclines with the residual silanol groups and thus avoids the appearance of tailed peaks. Detection was based on using an UV spectrophotometer and gradient elution with acetonitrile-oxalic acid as mobile phase permitted good separation of all the peaks. Specificity was demonstrated by the retention characteristics, UV spectra and peak purity index. Linearity, precision, recovery and sensitivity were satisfactory. The procedure was applied to the analysis of tetracycline residues (tetracycline, oxytetracycline (OTC), chlortetracycline (CTC), doxycycline (DC), minocycline (MINO) and methacycline (MTC)) in honey of different types. Extraction involved using a mild acidic solvent containing EDTA to release protein-bound or sugar-bound tetracyclines. For the clean-up step, solid phase extraction using phenyl cartridges was applied. Detection limits in the honey using the proposed procedure are between 15 and 30 ng g(-1), depending on the tetracycline.     

Molecularly imprinted SPE and MEKC with in-capillary sample preconcentration for the determination of digoxin in human urine

Molecularly imprinted solid-phase extraction (MISPE) combined with MEKC was used for clean-up, preconcentration and determination of digoxin in the presence of its aglycon digoxin (digoxigenin) in human urine samples. In addition, the use of an in-capillary sample concentration electrophoretic technique by sweeping was investigated to enhance the concentration sensitivity in MEKC. The highly selective, fast and effective sample pretreatment by MISPE along with the preconcentration by sweeping could overcome the low sensitivity of the highly efficient capillary electrophoresis separation with UV detection. The optimization of the variables affecting the separation as well as MISPE conditions procedure was carried out to select the best conditions of selectivity and sensitivity to determine digoxin at low concentration levels in urine. To demonstrate the suitability of the developed method several analytical characteristics (selectivity, linearity, accuracy, precision, and LOD) were evaluated. Satisfactory results were obtained in terms of linearity (r > 0.99), recovery (95.4-96.5% with RSD from 1.3% to 2.6%), precision (RSD from 0.3% to 1.7% for migration times and from 2.1% to 7.3% for corrected peak areas), and sensitivity (LODs of 6 μg/L with 5 mL of sample or 1.2 μg/L with 25 mL). The proposed MISPE-MEKC method was satisfactorily applied to the analysis of spiked human urine samples achieving a concentration factor up to 7500-fold.     

Comparison of Three Analytical Methods for the Determination of Quinolones in Pig Muscle Samples

This work presents a comparison between three analytical methods developed for the simultaneous determination of eight quinolones regulated by the European Union (marbofloxacin, ciprofloxacin, danofloxacin, enrofloxacin, difloxacin, sarafloxacin, oxolinic acid and flumequine) in pig muscle, using liquid chromatography with fluorescence detection (LC–FD), liquid chromatography–mass spectrometry (LC–MS) and liquid chromatography-tandem mass spectrometry (LC–MS/MS). The procedures involve an extraction of the quinolones from the tissues, a step for clean–up and preconcentration of the analytes by solid-phase extraction and a subsequent liquid chromatographic analysis. The limits of detection of the methods ranged from 0.1 to 2.1 ng g⁻¹ using LC–FD, from 0.3 to 1.8 using LC–MS and from 0.2 to 0.3 using LC–MS/MS, while inter- and intra-day variability was under 15 % in all cases. Most of those data are notably lower than the maximum residue limits established by the European Union for quinolones in pig tissues. The methods have been applied for the determination of quinolones in six different commercial pig muscle samples purchased in different supermarkets located in the city of Granada (south-east Spain).

     

Phenolic compounds in Brassica vegetables

Phenolic compounds are a large group of phytochemicals widespread in the plant kingdom. Depending on their structure they can be classified into simple phenols, phenolic acids, hydroxycinnamic acid derivatives and flavonoids. Phenolic compounds have received considerable attention for being potentially protective factors against cancer and heart diseases, in part because of their potent antioxidative properties and their ubiquity in a wide range of commonly consumed foods of plant origin. The Brassicaceae family includes a wide range of horticultural crops, some of them with economic significance and extensively used in the diet throughout the world. The phenolic composition of Brassica vegetables has been recently investigated and, nowadays, the profile of different Brassica species is well established. Here, we review the significance of phenolic compounds as a source of beneficial compounds for human health and the influence of environmental conditions and processing mechanisms on the phenolic composition of Brassica vegetables.     

Crystal and molecular structure of three biologically active nitroindazoles

3-Bromo-1-methyl-7-nitro-1H-indazole (1), 3-bromo-2-methyl-7-nitro-2H-indazole (2) and 3,7-dinitro-1(2)H-indazole (3) have been synthesized and characterized by X-ray diffraction, ¹³C and ¹⁵N NMR spectroscopy in solution and in solid-state. The dihedral angles obtained in the crystal structures are in good agreement with the molecular parameters calculated using DFT B3LYP calculations employing the 6-311++G(d,p) basis set. Compounds 1 and 2 present intermolecular halogen bonds between the bromine and the oxygen atoms of the nitro group and in compound 3 inter- and intramolecular hydrogen bonding exists.     

Determination of cadmium,aluminium, and copper in beer and products used in its manufacture by electrothermal atomic absorption spectrometry

Procedures were developed for determining cadmium, aluminium, and copper in beer and the products used in its manufacture by electrothermal atomic absorption spectrometry. Beer samples were injected into the furnace and solid samples were introduced as suspensions after preparation in a medium containing hydrogen peroxide, nitric acid, and ammonium dihydrogen phosphate for cadmium atomization. Calibration was performed with aqueous standards, and characteristic masses and detection limits were, respectively, 1 and 0.3 pg for cadmium, 18 and 5.4 pg for aluminium, and 5.6 and 6.8 pg for copper. Different samples of beer, wort, brewer's yeast, malt, raw grain, and hops were analyzed by the proposed procedures. Cadmium was found in low concentrations (0.001-0.08 microg/g and 0-1.3 ng/mL); copper (3-13 microg/g and 25-137 ng/mL) and aluminium (0.6-9 microg/g and 0.1-2 microg/mL) were found at higher levels. The reliability of the procedure was confirmed by comparing the results obtained with others based on microwave oven sample digestion, and by analyzing several certified reference materials.