Advantages of LC–MS–MS compared to LC–MS for the determination of nitrofuran residues in honey

In the framework of developing analyses for exogenous contaminants in food matrices such as honey, we have compared data obtained by high-performance liquid chromatography coupled with mass spectrometry (LC–MS) to those provided by high-performance liquid chromatography and tandem mass spectrometry (LC–MS–MS). Initial results obtained with LC–MS showed that the technique lacked selectivity, which is why the method was validated by LC–MS–MS. This method involves a solid-phase extraction (SPE) of nitrofuran metabolites and nitrofuran parent drugs, a derivatization by 2-nitrobenzaldehyde for 17 h, and finally a clean-up by SPE. The data obtained show that the limits of detection varied between 0.2 and 0.6 μg kg⁻¹ for the metabolites and between 1 and 2 μg kg⁻¹ for nitrofuran parent drugs. The method was applied to different flower honeys. The results showed that nitrofurans (used as antibiotics) are consistently present in this matrix, the predominant compound being furazolidone. Figure Working bees     

New structures from the thermal rearrangement of polybutadiene revealed by 2D HSQC NMR

The thermal reactions of polybutadiene (PB) at 260 °C in inert atmosphere were followed by ¹H and ¹³C NMR spectroscopy. Within 24 h of heating, the change in the intensities of some peaks and the appearance of new peaks of NMR spectra permits to follow the reactions occurring in polybutadiene. The sample, after heating for 6 h, was then characterized by a two dimensional HSQC NMR spectrum, showing the appearance of CH₃CH moiety, and the migration of double bond in polybutadiene. From these results the new mechanism of intra/intermolecular reactions was proposed.     

New separation method for organic and inorganic selenium compounds based on anion exchange chromatography followed by inductively coupled plasma mass spectrometry

We describe a new method for separating the organic and inorganic selenocompounds methaneseleninic acid, selenite, selenate, methylselenocysteine, selenocystine as well as both selenomethionine and its oxidized form. The separation is performed on a Hamilton PRP-X100 column. According to the literature, the oxidized form of selenomethionine—which is easily formed—is eluted close to the dead volume when this column is used. The choice of parahydroxybenzoic acid as mobile phase enabled us to elute all of these species after this oxidized form, resulting in better identification and quantification. The factors determining separation (eluent concentration, pH, gradient) were optimized via an experimental design. Application of the method to yeast and commercial tablets showed that the principal Se compound present was selenomethionine, which was also present in its oxidized form.     

Dynamique Moléculaire des Chloro-4 et Bromo-4 Méthylènecyclohexanes par Résonance Magnétique Nucléaire du 13C

Kinetic parameters are obtained for ring inversion of 4-chloro- and 4-bromo-1-methylenecyclohexanes by observation of ¹³C and ¹H NMR spectra as a function of sample temperature. Cl and Br substituents show similar effects on the inversion barrier in the exo-methylene system and in the parent cyclohexane.     

RMN 13C de cyclanones halogénées. Détermination et additivité des incréments du chlore en série cyclohexanique

The ¹³C n.m.r. spectra of fourteen chlorocyclohexanones have been recorded to examine the variation of the ¹³C chemical shifts as a function of the position and the number of the chlorine substituents. Additivity relationships were found which enable reasonable prediction of the chemical shifts of chlorinated cyclohexanones. Comparison between the observed and calculated chemical shifts of mono- and dichlorinated flexible molecules shows that the chlorine effects are additive.     

Sur la tétrabromo-2, 2, 6, 6 méthyl-4 cyclohexanone: Mise en evidence d'un equilibre conformationnel par RMN à haut champ

High field n.m.r. spectra of 2,2,6,6-tetrabromo-4-methyl- and -4-tert-butylcyclohexanones ( 1 and 2 ) have been computed and simulated. From coupling constants (J_gem, J_ea, J_aa and ⁴J) and chemical shifts it is shown that 1 is in equilibrium in solution. This work supports the conclusions deduced from infrared data of 1 in the scissors vibration region δ(CH₃).     

Exemple d'une transposition dyotropique à l'état solide Mise en evidence par RMN haute résolution

The analysis of 250 MHz spectra of 2,3,6-tribromo-4-methyl-cyclohexanones gives the precise value of the J(H? H) coupling constants of these products. The validity of the assignments has been checked by computer simulation of the spectra. The results obtained have been interpreted in terms of geometric deformations.     

I. Etude de l'Influence de la Nature et de l'Orientation d'un Substituant sur les Constantes de Couplage en Série Tertiobutyl-4 Cyclohexanonique par RMN à Haut Champ

The 250 MHz proton spectra of six α-halogeno-4-tert-butylcyclohexanones have been recorded and the dependence of the coupling constants upon the nature, the position, the orientation and the number of substituents (C?O, Cl, t-Bu) has been examined. The results obtained are interpreted in terms of geometrical deformation or substituent effects.