Ionic liquids as mobile phase additives in high-performance liquid chromatography with electrochemical detection: Application to the determination of heterocyclic aromatic amines in meat-based infant foods

The beneficial effects of several ionic liquids (ILs) as mobile phase additives in high-performance liquid chromatography with electrochemical detection for the determination of six heterocyclic aromatic amines (HAs) have been evaluated for first-time. The studied ionic liquids were 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF₄), 1-hexyl-3-methylimidazolium tetrafluoroborate (HMIm-BF₄) and 1-methyl-3-octylimidazolium tetrafluoroborate (MOIm-BF₄). Several chromatographic parameters have been evaluated in the presence or absence of ILs, or using ammonium acetate as the most common mobile phase additive, with three different C18 stationary phases. The effect of the acetonitrile content was also addressed. In general, best resolution, lower peak-widths (up to 72.1% lower) and lower retention factors are obtained when using ILs rather than ammonium acetate as mobile phase additives. The main improvement was obtained in the baseline noise, being 360% less noisy for BMIm-BF₄, 310% for HMIm-BF₄, and 227% for MOIm-BF₄, when compared to ammonium acetate at +1000 mV. Different chromatographic methods using the best conditions for each IL were also evaluated and compared. Finally, the best chromatographic conditions using 1 mM of BMIm-BF₄ as mobile phase additive, the Nova-Pak^® C18 column, 19% (v/v) of acetonitrile content in the mobile phase, and +1000 mV in the ECD, have been applied for the chromatographic analysis of six HAs contained in meat-based infant foods. The whole extraction method of meat-based infant foods using focused microwave-assisted extraction and solid-phase extraction has also been optimized. Extraction efficiencies up to 89% and detection limits ranged between 9.30 and 0.165 ng g⁻¹ have been obtained under optimized conditions.     

Research about transmission of the mechanical vibration done by machine-tools on the group of bones shoulder-neck-head

Different researches have shown that long–term exposure to whole–body vibration can induce different injuries like back pain, injuries of the different part of the body, disturbing the physical and intellectual activities. The resulted diseases could be occasional or could be for ever. Bearing in mind that vibration is applied on the hand or feet, the health rick can be assessed if the forces transmitted in the shoulder during vibration are known. To estimate the forces a biomechanical model has been developed in which the shoulder, neck and head are represented by rigid bodies. The bodies are connected by visco–elastic joint elements. The applied forces are resulted from experimental measurements. To assess the health risk the forces must be divised in two components, an ascendant one and a descendent one. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Mechanical Stability for the Hand-Arm System

The present paper contains a study regarding importance stability in the mechanical systems, mechanical systems are emerging under mechanical vibrations action, it referring especially to the human hand–arm system. Mechanical systems stability is directly influenced of the dumper and the elasticity factors. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantification of p-cresol sulphate in human plasma by selected reaction monitoring

Chronic renal failure patients accumulate in the blood molecules that are normally excreted into the urine. p-Cresol Sulphate (pCS), the most representative retained toxin, shows a high level of toxicity. Therefore, its quantification could represent a prediction factor to determine the risk of endothelial dysfunction and cardiovascular complication and response to the haemodialysis treatment. The aim of this study was to evaluate the suitability of the multiple reaction monitoring (MRM) technique in order to improve the sensibility, the selectivity and the timing of pCS detection in a small amount of plasma. Deproteinized plasma of uremic patients was concentrated and dissolved in liquid chromatography (LC) mobile phase solution. pCS was quantified by LC coupled to tandem mass spectrometry (LC-MS/MS) on a triple-quadrupole mass spectrometer. Selective and sensitive detection of pCS was achieved by selecting the specific parent ion and monitoring two specific fragment ions. The MRM assay was carried out using the following transitions: m/z 187?→?80.00 and m/z 187?→?107.00. A good linearity was observed for each calibration curve. The intra-day and inter-day results showed a good precision and repeatability. The percentage recoveries indicate an optimal selectivity of the analytical method. The MRM assay to quantify pCS in a small amount of human plasma is rapid, highly sensitive, selective and with a good repeatability.     

Further Insight into the Photostability of the Pyrene Fluorophore in Halogenated Solvents

Pyrene fluorophores of pyrene‐functionalized CdSe quantum dots (QD@Py), as well as alkylpyrene and pyrene itself (Py), undergo fast degradation in aerated chloroform under ultraviolet‐A (UV‐A, 316<λ<400 nm) illumination. Steady‐state fluorescence studies of irradiated chloroform solutions of QD@Py show formation of new bands, red‐shifted compared to that of the pyrene moiety. Similar behaviour is observed for pyrene and the alkylpyrene system. Column chromatography of the pyrene photolysate in chloroform allowed us to isolate photoproducts arising from pyrene degradation, and to obtain information on the structure of the photoproducts responsible for the emission bands. The most predominant photoproducts were those originating from the reaction of pyrene with dichloromethyl radicals. The phototransformation of QD@Py and the alkylpyrene involves mainly detachment of the alkyl chain from the aromatic ring, induced also by dichloromethyl radicals, and oxidation of the alkyl chain at the benzylic position was detected as well. By contrast, these pyrene systems show a high photostability in aerated dichloromethane. Transient absorption measurements showed formation of both pyrene triplet and pyrene radical cation for all pyrene systems in these halogenated solvents. The yield of pyrene radical cations for Py is higher than for QD@Py and the alkylpyrene. In addition, pyrene radical cations were longer‐lived in dichloromethane than in chloroform. The reason for the pyrene photostability in dichloromethane is the different reactivity of chloromethyl and dichloromethyl radicals towards pyrene and oxygen. These studies show that the use of dichloromethane can be a suitable alternative to chloroform when the good solubility properties of these halogenated solvents are needed to dissolve pyrene when this chromophore is used as a fluorescent probe.     

Ring-opening polymerization of epoxides catalyzed by uranyl complexes: an experimental and theoretical study of the reaction mechanism

A comprehensive computational study on the ring-opening polymerization of propylene oxide catalyzed by uranyl chloride [UO(2)Cl(2)(THF)(3)] and the uranyl aryloxide [UO(2)(OAr)(2)(THF)(2)] (Ar = 2,6-(t)Bu(2)C(6)H(3)) is reported. The initiation and propagation steps have been probed and significant differences between the two catalysts discovered. The initiation step involving uranyl chloride is an intermolecular process because the orientation of the lone pair on the initiating chloride nucleophile is optimally oriented toward the empty σ*-antibonding orbital of the epoxide, which lowers the activation barrier by 22 kcal mol(-1). Thus, initiation is orbitally controlled. Propagation occurs through a dimeric species, and low-temperature fluorescence spectroscopy has been used to probe this experimentally. In contrast the initiation step for the uranyl aryloxide catalyzed mechanism is intramolecular because of the steric constraints imposed by the bulky substituents on the aryl ring and the fact that the lone pair on the nucleophile is able to approach the propylene oxide coordinated to the same uranium center. Thus, initiation is principally sterically controlled. Propagation is, however, intermolecular, and this can be traced to steric effects. Experimental evidence in the form of fluorescence spectroscopy and diffusion NMR has been used to explore the propagation process in solution.     

Thermal expansion and optical length variation of sodium β-alumina along the c-axis

Thermal expansion and the optical length variation have been measured for a single crystal sodium β-alumina, along the c-axis. A laser interferometer has been used in the measurement. The measurements of the length and optical length variation do not indicate any anomalous behavior. The thermal expansion and thermooptic coefficients vary smoothly like the ionic conductivity and do not display any indication of cooperative effects.     

Surface properties of some carotenoids spread in monolayers at the air/water interface. Experimental and computational approach

The surface pressure versus molecular area isotherms of some carotenoids: β,β-carotene-4-one (echinenone, ECH), β,β-carotene-4,4′-dione (canthaxanthin, CAN) and 4,4′-diapo-ω,ω-carotene-4,4′-dial (APO), spread at the air/water interface, are reported. A van der Waals type state equation is used to describe the high molecular area portions of the compression isotherms and interaction parameters within monolayers are derived. Quantum chemical semi-empirical SCF MO calculations (AM1 and PM3) are performed for the optimized geometries of molecules and dipole moments are calculated. Similar theoretical magnitudes are obtained by both methods. Surface properties, like collapse pressure, surface compressional modulus and interaction parameters are discussed in terms of dipole-dipole interactions, and correlations with the calculated quantities for the carotenoid molecules are analyzed. The orientation of the different carotenoid molecules in the monolayer is discussed.