Rapid determination of aliphatic amines in water samples by pressure-assisted monolithic octadecylsilica capillary electrochromatography-mass spectrometry

A pressure-assisted capillary chromatography-mass spectrometry method based on the use of a monolithic octadecylsilica (ODS) capillary is proposed for the determination of aliphatic amines. A 25 mM citric acid buffer containing 10% methanol is used as running electrolyte. Separation is achieved by simultaneously applying a capillary electrophoresis (CE) voltage of 13 kV and an overimposed pressure of 8 bar. The use of pressure is required to ensure stable electrospray conditions. Analysis times are reduced by using a capillary column consisting of a 30 cm long monolithic silica capillary column bound with ODS and a fused-silica capillary column also 30 cm long. The proposed method was successfully applied to the determination of low-molecular-weight aliphatic amines in tap and river water. The analysis of real samples requires cleanup and preconcentration, which can be performed automatically by inserting a minicolumn in the replenishment system of the commercial instrument.     

Contributions to the determination of histamine rate by measuring out the histamine-orthophthalaldehyde complex in the absorption and fluorescence

Histamine is an important compound from a physiological point of view, but it is toxic since the absorption of low amounts of histamine can cause abdominal pains accompanied with vomiting. Why we have developed a new method for histamine analysis in order to improve Lerke and Bell method. From the absorption spectra, we showed that the stoichiometry of the complex histamine-orthophthalaldehyde (OPA) is 1:1. From the emission spectra, it was observed that the complex fluorescence is inhibited in acidic medium. In alkaline medium, an exaltation of fluorescence was observed, but the complex histamine-OPA was unstable. Nevertheless, kinetic study showed that good linear correlations between the fluorescence maxima of the formed complex and the histamine concentration could be obtained in this alkaline medium.     

Assays for total homocysteine and other thiols by capillary electrophoresis-laser-induced fluorescence detection. I. Preanalytical condition studies

In recent papers, we presented a new analytical method for thiol quantification in serum. It is based on the use of capillary electrophoresis and laser-induced fluorescence to analyze thiol 6-iodoacetamidofluoresceine (IAF) derivatives. Quantitative results of homocysteine, glutathione, cysteine-glycin, and cysteine were shown (Clin. Chem. 45 (1999) 412). A comprehensive comparison of the quantitation of homocysteine in serum, using high-performance liquid chromatography/conventional fluorescence detection and fluorescence polarization immunoassay was also used (E. Caussé et al., Electrophoresis 21 (2000) 2074). Sample preparation prior to derivatization with IAF had never been investigated. In this work we present the results of quantitation of thiols in serum and plasma with three different anticoagulants widely used: ethylenediaminetetraacetic acid (EDTA), heparin, and sodium citrate. We show that serum and EDTA plasma gave the same results. Then serum protein precipitations by acetonitrile, acetone, sulfosalicylic acid, perchloric acid and trichloracetic acid, prior to derivatization by IAF, were also investigated. Their influence on the concentrations of the thiols were determined. Sulfosalicylic acid and acetonitrile precipitations are well adapted, whereas acetone cannot be used.     

The electrophilic reactions of pentacyanonitrosylferrate(II) with hydrazine and substituted derivatives. Catalytic reduction of nitrite and theoretical prediction of eta(1)-, eta(2)-N(2)O bound intermediates

The electrophilic reactivity of the pentacyanonitrosylferrate(II) ion, [Fe(CN)(5)NO](2)(-), toward hydrazine (Hz) and substituted hydrazines (MeHz, 1,1-Me(2)Hz, and 1,2-Me(2)Hz) has been studied by means of stoichiometric and kinetic experiments (pH 6-10). The reaction of Hz led to N(2)O and NH(3), with similar paths for MeHz and 1,1-Me(2)Hz, which form the corresponding amines. A parallel path has been found for MeHz, leading to N(2)O, N(2), and MeOH. The reaction of 1,2-Me(2)Hz follows a different route, characterized by azomethane formation (MeNNMe), full reduction of nitrosyl to NH(3), and intermediate detection of [Fe(CN)(5)NO](3)(-). In the above reactions, [Fe(CN)(5)H(2)O](3)(-) was always a product, allowing the system to proceed catalytically for nitrite reduction, an issue relevant in relation to the behavior of the nitrite and nitric oxide reductase enzymes. The mechanism comprises initial reversible adduct formation through the binding of the nucleophile to the N-atom of nitrosyl. The adducts decompose through OH(-) attack giving the final products, without intermediate detection. Rate constants for the adduct-formation steps (k = 0.43 M(-)(1) s(-)(1), 25 degrees C for Hz) decrease with methylation by about an order of magnitude. Among the different systems studied, one-, two-, and multielectron reductions of bound NO(+) are analyzed comparatively, with consideration of the role of NO, HNO (nitroxyl), and hydroxylamine as bound intermediates. A DFT study (B3LYP) of the reaction profile allows one to characterize intermediates in the potential hypersurface. These are the initial adducts, as well as their decomposition products, the eta(1)- and eta(2)-linkage isomers of N(2)O.     

Synthesis of gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids from fragmentation of gamma- and delta-lactones

A noncoded amino acid of cyclomarin A (1) was synthesized in a racemic fashion. The method employs a six-membered ring template to control the relative stereochemistry and introduction of the functional groups. Ultimately, Pd-catalyzed fragmentation of the lactone provided gamma,delta-unsaturated and delta,epsilon-unsaturated alpha-amino acids. A Pd-catalyzed ring opening of a gamma-lactone is also reported.     

Le problème de la réduction des intégrales électroniques dans la méthode L.C.A.O. améliorée

Résumé L'auteur reprend les principes de la méthode L.C.A.O. améliorée en vue d'une justification plus complète des procédés employés. La théorie des perturbations permet d'une façon simple de tenir compte de la corrélation entre les électrons grâce à l'introduction d'une fonction universelle de la distance entre deux électrons. Le problème est ainsi ramené de l'échelle moléculaire à l'échelle atomique. On montre que la corrélation entre les électrons entraîne la réduction des intégrales atomiques. Le problème de la réduction des intégrales coulombiennes est traité en détail. La possibilité de négliger les autres intégrales biélectroniques est ensuite examiné. Enfin est étudié le problème de la réduction des intégrales de coeur.

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The principles of the improved LCAO theory are investigated to give a better justification for its methods. Perturbation theory allows a simple account for electronic correlation, when a universal function of interelectronic distance is introduced. The problem is hereby reduced from molecular to atomic scale. The reduction of electronic energy integrals by correlation is shown, especially for Coulomb integrals. The possibility of neglecting the other bielectronic integrals is examined. Finally the problem of core integral reduction is studied.

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Zusammenfassung Die Grundlagen der verbesserten LCAO-Methode werden untersucht, um dieses Verfahren besser zu rechtfertigen. Mit einer allgemeinen Funktion des Abstandes je zweier Elektronen und der Störungstheorie läßt sich die Elektronenkorrelation auf einfache Weise berücksichtigen. Damit wird das Problem vom molekularen auf den atomaren Maßstab zurückgeführt. Die Elektronenkorrelation bringt eine Reduktion der Elektronenenergieintegrale mit sich; die Coulombintegrale werden im einzelnen behandelt. Anschließend wird die Möglichkeit untersucht, die übrigen Zweielektronenintegrale zu vernachlässigen. Schließlich wird die Reduktion der Rumpfintegrale behandelt.

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Nous tenons à remercier très vivement le Docteur Chr. K. Jørgensen (Cyanamid European Research Institut, Genève) pour les intéressants échanges de vue que nous avons eu sur les divers problèmes évoqués dans cet article ainsi que le Docteur G. Berthier (Institut de Biochimie théorique, Paris) et Monsieur H. v. Hirschhausen.     

Sample preparation improvement in polycyclic aromatic hydrocarbons determination in olive oils by gel permeation chromatography and liquid chromatography with fluorescence detection

The determination of 15 polycyclic aromatic hydrocarbons (PAHs) in olive oil samples has been improved in order to obtain a fast methodology with a low limit of detection through the combination of liquid-liquid extraction with acetonitrile and preparative gel permeation chromatography (GPC) prior to the injection of purified extracts into a C18 column. Acetonitrile-water was used as the mobile phase with a gradient from 50 to 95%, w/w, acetonitrile in 30 min. The oven temperature was maintained at 15 degrees C, and fluorometric detection was made at a fixed excitation wavelength of 264 nm and variable, optimal emission wavelength for each analyte ranging from 352 nm for 11-H-benzo(b)fluorene to 500 nm for indeno(1,2,3-cd)pyrene. Recovery for all the compounds studied varied from 75 to 111%, and limit of detection values from 0.05 ng/g for benzo(k)fluoranthene to 0.48 ng/g for indeno(1,2,3-cd)pyrene, corresponding to 0.09 ng/g benzo(a)pyrene. Results were compared with those obtained by liquid-liquid extraction followed by a cleanup on silica and a direct GPC treatment of oil samples diluted in dichloromethane, 2 other methodologies that are appropriate for quantifying PAHs in olive oils. However, the proposed method improves the determination limits, reduces the time of analysis, and provides a highly stable baseline for sample chromatograms.     

Development and validation of an analytical method for detection of estrogens in water

An analytical procedure enabling routine analysis of four environmental estrogens at concentrations below 1 ng L^–1 in estuarine water samples has been developed and validated. The method includes extraction of water samples using solid-phase extraction discs and detection by gas chromatography (GC) with tandem mass spectrometry (MS–MS) in electron-impact (EI) mode. The targeted estrogens included 17- and 17-estradiol (aE2, bE2), estrone (E1), and 17-ethinylestradiol (EE2), all known environmental endocrine disruptors. Method performance characteristics, for example trueness, recovery, calibration, precision, accuracy, limit of quantification (LOQ), and the stability of the compounds are presented for each of the selected estrogens. Application of the procedure to water samples from the Scheldt estuary (Belgium – The Netherlands), a polluted estuary with reported incidences of environmental endocrine disruption, revealed that E1 was detected most frequently at concentrations up to 7 ng L^–1. aE2 was detected once only and concentrations of bE2 and EE2 were below the LOQ.Presented at the 9th FECS Conference on Chemistry and the Environment, Bordeaux, France, 29 August–1 September 2004     

Spontaneous dissolution of a single-wall carbon nanotube salt

Upon reduction with alkali metals, single-wall carbon nanotubes (SWNTS) are shown to form polyelectrolyte salts that are soluble in polar organic solvents without any sonication, use of surfactants, or functionalization whatsoever, thus forming true thermodynamically stable solutions of naked SWNTs.     

Determination of polycyclic aromatic hydrocarbons in honey by matrix solid-phase dispersion and gas chromatography/mass spectrometry

A multiresidue method was developed for the de termination of 16 polycyclic aromatic hydrocarbons (PAHs) in unifloral and multifloral honeys. The analytical procedure is based on the matrix solid-phase dispersion of honey on a mixture of Florisil and anhydrous sodium sulfate in small glass columns and extraction with hexane-ethyl acetate (90 + 10, v/v) with assisted sonication. The PAH residues are determined by gas chromatography with mass spectrometric detection using selected-ion monitoring. Average recoveries for all the PAHs studied were in the range of almost 80 to 101%, with relative standard deviations of 6 to 15%. The limits of detection ranged from 0.04 to 2.9 microg/kg. The simultaneous extraction and cleanup of samples makes this method simple and rapid, with low consumption of organic solvents