Fast screening of anabolic steroids and other banned doping substances in human urine by gas chromatography/tandem mass spectrometry

A fast and sensitive method for the comprehensive screening of anabolic agents and other banned doping substances using gas chromatography/tandem mass spectrometry (GC/MS/MS) with an external ionization ion trap mass spectrometer is presented. The method takes advantage of the resolving power of MS/MS to eliminate background interferences, thus speeding up the chromatographic analysis. For each compound, different fragmentation reactions were studied and their collision energies optimized to obtain the best sensitivity in terms of their signal-to-noise ratio (S/N). A dramatic reduction in overall analysis time was achieved compared with other common approaches. More than 50 substances could finally be monitored in less than 7.4 min with detection limits (S/N >3) lower than 0.5 ng ml(-1) for most of the compounds with special sensitivity requirements according to the International Olympic Committee (IOC). A validation procedure for qualitative analysis was performed. The selectivity of the method showed that no interfering peaks were observed at the retention time of the analytes. Good intermediate precision, below 25% for most of the compounds, and robustness were observed. The optimized method was successfully applied to analyse more than 100 real human urine samples with optimum sensitivity and specificity rates.     

Lanthanide nitrate complexes with 2-azacyclononanone

Thermal behavior of rare earth nitrate complexes with 2-azacyclononanone (AZA) with Ln(NO₃)₃·3(AZA) composition (where Ln=Gd, Er and Ho) was analyzed in kinetic point of view. Kinetic parameters were calculated from thermogravimetric data. All obtained results were similar. The first decomposition step was representative to the loss of ligand and the residue was essentially Ln₂O₃. Furthermore, a reaction path was proposed for the thermal decomposition of the Ln(NO₃)₃·3(AZA).     

Approximate transferability in alkanenitriles

The atomic and bond properties of a series of alkanenitriles were calculated in order to analyze the transferability of the CN, methyl, and methylene groups. The calculations were carried out using the atoms in molecules (AIM) theory on RHF/6‐31++G**// RHF/6‐31G** wave functions obtained for compounds CN–R (R ranging from H to C₁₁H₂₃). Linear correlations between L(Ω) and N(Ω) were used to establish N(CH₂) and N(CH₃) nearly transferable values. Average values and maximum differences to the mean value of several properties were used for classifying the CN group. It shows a transferable behavior along the CN–R series for R>Et. The methyl group presents specific properties when R<Pr. The methylene groups can be classified considering both their position with respect to the end of the chain and the position with respect to the CN group. The atomic energy displays a dependence on the molecular size. Although this behavior does not allow to consider this property as transferable, both the ab initio total electronic molecular energies and the experimental heats of formation can be fitted, by linear regression analysis, as a function of the number of methylene groups. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Topological study of intramolecular hydrogen bonding in beta-hydroxyethylperoxy radical and beta-hydroxyethoxy radical along its dissociation pathway

The presence of intramolecular hydrogen bond (IHB) in beta-hydroxyethylperoxy and beta-hydroxyethoxy radicals was investigated using the QTAIM topological study on UB3LYP/6-311++G(2d,2p) charge densities. Only one of the two conformers of beta-hydroxyethylperoxy radical which were previously considered to present IHB displays a bond critical point (BCP) associated to an IHB. Furthermore, the atomic energies and electron populations indicate no evidence of IHB in the second conformer. Nevertheless, very small differences in molecular energies were obtained using several one-step and multi-step methods (G3, G3B3) between both conformers. No BCP is found between the hydroxyl hydrogen and the oxygen in the most stable conformer or in the transition state for the dissociation path of beta-hydroxyethoxy radical. However, a BCP is formed in the last steps of this path, thereby yielding H-bonded products.     

Reagentless system for sulphite determination based on polyaniline

A new reagentless system for sulphite (or sulphur dioxide) determination is reported based on the use of an organic conducting polymer, polyaniline, and its absorbance variation at 550 nm, depending on the sulphite concentration. After chemical polymerisation of aniline a very thin film of polyaniline is obtained. Although the response is not fully reversible, each film can be used for at least 10 measurements for low analyte concentrations (up to 0.5 mg l⁻¹) and five measurements for higher sulphite concentrations. Moreover, the reproducibility, ease of preparation and low cost of the films, permit the use of a new disposable system for each measurement. When the change in absorbance at 550 nm was measured for 210 s (stabilisation time), the system showed a linear response, which ranged from 0.025 to 1.50 mg l⁻¹ of sulphite. A theory with regard to the reaction mechanism between the polyaniline films and sulphite is also proposed. The system was applied to sulphite determination in wine samples and the results were in agreement with those obtained by the Official Method of Analysis (iodometric titration).     

Intermolecular hydroamination and hydroarylation reactions of alkenes in ionic liquids

Intermolecular hydroamination or hydroarylation reactions of norbornene and cyclohexadiene performed with catalytic amounts of Brönsted or Lewis acid in ionic liquids were found to provide higher selectivity and yields than those performed in classical organic solvents. The ionic liquid increases the acidity of the media and stabilizes ionic intermediates through the formation of supramolecular aggregates.