Analyse destructive de traces de rubidium dans des echantillons mineralogiques par radioactivation au moyen de neutrons de 14 MeV

Increasing interest is devoted in geochemistry to the determination of minor elements in rocks and minerals with the best analytical precision. The use of different methods is quite useful to point out and overcome the systematic and specific interferences of the geological matrix. 14 MeV neutron activation analysis can be used for such a purpose as an additional check method. A successful attempt has been made in the determination of rubidium in different geochemical standards. A sensitivity of 100 ppm can be reached with a 5% precision without any interference problem.     

Identification,synthesis and conformational study of a CN(R,S) synthon by-product: (5R, 10R)-5,10-diphenyl-1,6-diaza-3,8-dioxabicyclo[4.4.1]undecane

The title compound, containing a new heterocyclic skeleton, was identified by X-ray crystallography as the product of condensation of (R)-phenylglycinol with an excess of formaldehyde. The molecule adopts a rigid double twist-chair conformation in both solid and solution states.     

Mobile-phase-viscosity dependence on DNA separation in slalom chromatography

Slalom chromatography (SC) is an alternative chromatographic procedure for the separation of relatively large double-stranded DNA molecules and is based on a new principle. The retardation of the DNA fragments from the cleavage of the Lambda DNA by the KpnI restriction enzyme was studied using an acetonitrile-phosphate buffer as a mobile phase with various concentrations of viscosity modifier (i.e. glycerol) and a C1 column as a stationary phase. The DNA molecule retention was accurately described over the glycerol concentration range using a model previously established. It was shown that the eluent viscosity increase enhanced the slalom chromatographic capacity to separate the DNA fragments. A connection between SC and 'hydrodynamic chromatography' processes was predicted to link the two processes in a global separation mechanism based on a non-equilibrium principle.     

Protected Amine Labels: A Versatile Molecular Scaffold for Multiplexed Nominal Mass and Sub-Da Isotopologue Quantitative Proteomic Reagents

We assemble a versatile molecular scaffold from simple building blocks to create binary and multiplexed stable isotope reagents for quantitative mass spectrometry. Termed Protected Amine Labels (PAL), these reagents offer multiple analytical figures of merit including, (1) robust targeting of peptide N-termini and lysyl side chains, (2) optimal mass spectrometry ionization efficiency through regeneration of primary amines on labeled peptides, (3) an amino acid-based mass tag that incorporates heavy isotopes of carbon, nitrogen, and oxygen to ensure matched physicochemical and MS/MS fragmentation behavior among labeled peptides, and (4) a molecularly efficient architecture, in which the majority of hetero-atom centers can be used to synthesize a variety of nominal mass and sub-Da isotopologue stable isotope reagents. We demonstrate the performance of these reagents in well-established strategies whereby up to four channels of peptide isotopomers, each separated by 4 Da, are quantified in MS-level scans with accuracies comparable to current commercial reagents. In addition, we utilize the PAL scaffold to create isotopologue reagents in which labeled peptide analogs differ in mass based on the binding energy in carbon and nitrogen nuclei, thereby allowing quantification based on MS or MS/MS spectra. We demonstrate accurate quantification for reagents that support 6-plex labeling and propose extension of this scheme to 9-channels based on a similar PAL scaffold. Finally, we provide exemplar data that extend the application of isotopologe-based quantification reagents to medium resolution, quadrupole time-of-flight mass spectrometers.

Chemometric method to optimize chiral separation of imidazole derivatives by capillary electrophoresis

A chemometric methodology was proposed to optimize the migration time, height equivalent to a theoretical plate and separation of a mixture of a series of imidazole compounds by capillary electrophoresis. The optimization process was based on a special polynomial from 9 or 18 preliminary experiments. This method connects a general simplex method to a computer. A simplex two or three optimization-capillary electrophoresis (STO-CE) method has been developed in our laboratory. The most efficient separation was achieved with acetonitrile-phosphate buffer, pH 4.70, (5.30+94.70 (v/v)) with a beta-cyclodextrin concentration in the background electrolyte equal to 5.80 mM and a capillary temperature of 35 degrees C. Similar results were obtained using simple step-wise scanning. The higher relative difference obtained for these values with these two methods (simplex and step-wise scanning) was 5% for the beta-cyclodextrin concentration factor.     

Chiral discrimination ofN-(dansyl)-dl-amino acids on human serum albumin stationary phase: Effect of a mobile phase modifier

Summary The effect of perchlorate anion as mobile phase modifier on the separation factor, α, forN-(dansyl)-dl-norvaline andN-(dansyl)-dl-tryptophan on a human serum albumin (HSA) column was studied by varying the concentration,c, of the chaotropic agent and the column temperatureT. Gibbs-Helmholtz parameters Δ(ΔH) and Δ(ΔS) between thed andl enantiomers were determined from linear van't Hoff plots of lnα against 1/T. Thermodynamic results indicated that the enhancement of the separation factor observed asc was increased was enthalpically controlled owing to stereoselective H-bonding interactions. Such behavior was used to optimize the chromatographic conditions for separation ofN-(dansyl)-amino acids on HSA.     

Gamma-ray spectra and sensitivities for 2.8 MeV neutron activation analysis

The use of 2.8 MeV neutrons produced by the D(d, n)³He reaction should be taken into consideration in some applications of radioactivation analysis. The low number of elements activable by these neutrons makes possible to minimize the matrix interference and the background below the characteristic photopeaks. The very low dead-time of the spectrometric measurements permits the use of the maximum neutron flux available now and in the future. The purpose of this paper is to define experimentally the sensitivity of determination for the 16 main elements activable with a 400 keV Van de Graaff accelerator at a 2.8 MeV neutron flux of 2·10⁶ n·cm⁻²·sec⁻¹ on the sample.