Études sur la détection,la caractérisation et le dosage des aldéhydes: Méthodes d'oximation

Five methods for the estimation of aldehydes by oximation have been compared. In all the methods, a single or double branching in position α in the case of aliphatic aldehydes, and in positions 2 and 6 in the case of aromatic aldehydes, tends to lessen the accuracy (steric hindrance). Of the methods examined those of Bryant and Smith¹ and Smith and Mitchell³ are the most common.Three new oximes are described. For one of these, two modifications have been isolated, both of which are converted to acetate by the action of acetic anhydride and sodium carbonate. The question is discussed whether this is a case of the syn and anti forms of the oximo or of two polymorphic modifications.     

Vibrationally resolved photoabsorption spectroscopy of red fluorescent protein chromophore anions

Photoabsorption studies of red fluorescent protein chromophore anions have been performed at the ELISA electrostatic heavy-ion storage ring. The broad absorption band due to electronic excitation of the chromophores is tuned to a longer wavelength (redshifted) by extending the electronic conjugation of the molecule. A clear vibrational progression is resolved with E(vib) approximately 380 and 520 cm(-1) for two different forms of the chromophore. The vibrational modes correspond to collective motions of the entire molecular structure. It is argued that the excited electronic state has an equilibrium configuration far from that of the electronic ground state, i.e., poor Franck Condon overlap.     

Membrane-introduction mass spectrometry (MIMS)

Membrane-introduction mass spectrometry (MIMS) for chemical analysis involves directly sampling analytes in gaseous, liquid and solid samples through a semi-permeable membrane coupled to a mass spectrometer, yielding selective and sensitive quantitation. Because MIMS is an on-line technique, in which samples can be continuously flowed over a membrane interface, it can yield analytical results in real time without the need for sample clean-up and chromatographic separation. This review highlights trends and developments in MIMS over the past decade and describes recent studies that pertain to its use for on-site, in-situ and in-vivo chemical analysis. We report on advancements in instrumentation, including membrane materials, interface configurations and ionization techniques that have extended the range of analytes amenable to MIMS.We summarize the progress made in the miniaturization of mass spectrometers that have resulted in field-portable systems and review recent applications of continuous mobile monitoring and on-site environmental monitoring to yield both temporally and spatially resolved quantitative and semi-quantitative data. Finally, we describe recent work involving the use of MIMS for in-vivo chemical analysis.     

Ionization suppression effects with condensed phase membrane introduction mass spectrometry: methods to increase the linear dynamic range and sensitivity

Condensed phase membrane introduction mass spectrometry (CP‐MIMS) is an online analytical method that allows for the direct, trace level measurement of a wide range of analytes in complex samples. The technique employs a semi‐permeable membrane that transfers analytes from a sample into a flowing acceptor solvent, which is directly infused to an atmospheric pressure ionization source, such as electrospray or atmospheric pressure chemical ionization. While CP‐MIMS and variants of the technique have been in the literature for nearly a decade, much of the work has focused on instrument development. Few studies have thoroughly addressed quantitative methods related to detection limits, ionization suppression, or linear dynamic range. We examine ionization suppression in the direct rapid quantitation of analytes by CP‐MIMS and introduce several analytical strategies to mitigate these effects, including the novel implementation of a continuously infused internal standard in the acceptor phase solvent, and modulation of acceptor phase flow rate. Several representative analytes were used to evaluate this approach with spiked, complex sample matrices, including primary wastewater effluent and artificial urine. Also reported are improved measured detection limits in the low part‐per‐trillion range, using a ‘stopped‐flow’ acceptor mode. Copyright © 2015 John Wiley & Sons, Ltd.     

Development and validation of an SPE methodology combined with LC-MS/MS for the determination of four ionophores in aqueous environmental matrices

A multi-residue analytical methodology has been established for the determination of the four ionophores: lasalocid, monensin, salinomycin and narasin in aqueous environmental matrices, using nigericin as internal standard. The samples were filtrated prior to solid phase extraction. All compounds were measured using liquid chromatography coupled to tandem mass spectrometry applying electro spray ionisation. The absolute recoveries ranged from 92 to 110% (relative standard deviation: 2–14%) for spiked river water. The final method allowed for detection of ionophores down to a few ng/L in natural water bodies with LOQs for the entire methodology being 40, 49, 67, and 14 ng/L for lasalocid, monensin, salinomycin, and narasin, respectively.     

High-pressure Raman and infrared spectroscopic studies of ZrP2O7

High-pressure Raman and mid-infrared spectroscopic studies were carried out on ZrP₂O₇ to 23.2 and 13 GPa respectively. In the pressure range 0.7–4.3 GPa the lattice mode at 248 cm^?1 disappears, new modes appear around 380 and 1111 cm^?1 and the strong symmetric stretching mode at 476 cm^?1 softens, possibly indicating a subtle phase transition. Above 8 GPa all the modes broaden, and all of the Raman modes disappear beyond 18 GPa. On decompression from the highest pressure, 23.2, to 0 GPa all of the modes reappear but with larger full width at half maximum. Lattice dynamics of the high temperature phase of ZrP₂O₇ were studied using first principles method and compared with experimental values.