Separation of monosaccharides by hydrophilic interaction chromatography with evaporative light scattering detection

Hydrophilic interaction liquid chromatography (HILIC) was used to separate monosaccharides that are common in N-linked oligosaccharides in glycoproteins and other compounds. A TSKgel Amide-80 column was eluted with 82% acetonitrile, in 5 mM ammonium formate (pH 5.5). Column temperature was 60 degrees C and evaporative light scattering was used for detection (ELSD). With this method, L-fucose, D-galactose, D-mannose, N-acetyl-D-glucosamine, N-acetylneuraminic acid, and D-glucuronic acid were separated, with detection limits of 0.3-0.5 microg for each monosaccharide, and intermediate precisions were 3-6% RSD (n=6).     

Microassay for the simultaneous determination of cocaine, norcocaine, benzoylecgonine and benzoylnorecgonine by high-performance liquid chromatography

An improved method for the simultaneous determination of cocaine, norcocaine, benzoylecgonine and benzoylnorecgonine using reversed-phase high-performance liquid chromatography with ultraviolet detection is described. Following solid-phase extraction, chromatography was performed using a column containing an octadecylsilica-coated packing, eluted with 6% acetonitrile in phosphate buffer, pH 2.1, and detected at 233 nm. Using 80-microliters samples, the detection limit is 18 ng/ml for benzoylecgonine and benzoylenorecgonine and 35 ng/ml for cocaine and norcocaine. The coefficients of variation range from 3.5% (benzoylecgonine) to 7.0% (norcocaine). The procedure has been applied to samples of guinea pig plasma, urine and amniotic fluid and human urine.     

Relationship between enantioselectivity and solute structure on a chiral α1-acid glycoprotein column

Summary The relationship between the enantioselectivity, the retention and the solute structure for N-aminoalkylsuccinimides and 1-alkyl-2′,6′-pipecoloxylidides have been studied using α₁-acid glycoprotein as the chiral stationary phase. Both the enantioselectivity and the retention are highly affected by small changes of the solute structure in series of homologous compounds. For example, increasing the steric bulk on a basic aliphatic nitrogen improves the enantioselectivity. It was also demonstrated for the succinimides that the magnitude of the separation factor was highly affected by the distance between the basic nitrogen and the chiral center. The chiral selectivity was not lost for the succinimides despite the fact that the basic nitrogen was separated from the chiral center with seven atoms, which may be an effect of that these compounds contain more than one strong hydrogen bonding group. Substitution in the aromatic ring of the succinimides also influences both the retention and the chiral selectivity to a large extent. Electronegative substituents can increase the separation factor but introduction of an alkyl or an alkoxy group in the aromatic ring decreases the enantioselectivity for the succinimides.     

Vacancies in metals: from first-principles calculations to experimental data

We have revealed, and resolved, an apparent inability of density functional theory, within the local density and generalized gradient approximations, to describe vacancies in Al accurately and consistently. The shortcoming is due to electron correlation effects near electronic edges and we show how to correct for them. We find that the divacancy in Al is energetically unstable and we show that anharmonic atomic vibrations explain the non-Arrhenius temperature dependence of the vacancy concentration.     

Experimental analysis of low-Reynolds number free jets

The present paper analyzes the features of a low-Reynolds number free submerged jet with special regard to statistical quantities on the jet centerline. Measurements in an environment with very low disturbances allowed to observe details of turbulence and higher-order moments. Some peculiar features of the measured (natural) jet are shown to be in correspondence to observations referring to forced higher-Reynolds number jets. In particular, it is shown that, at low Reynolds numbers, the initial region of the jet is dominated by well-defined vortices in the shear layer. This result is substantiated by both the statistical moments and the spectral analysis. The presence of two distinct regimes is evidenced and discussed from a physical standpoint, also in relation to the mathematical analysis of the jet structure from the bibliography.

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Techniques for neuropeptide determination

Because immunoassay responds to epitopes, and many molecules share the same peptide epitope, it is very difficult to obtain an accurate understanding of peptides, their creation and hydrolysis, in biological systems. Separate-and-detect approaches have merit in that the many active peptides and inactive fragments of a particular system can be separately determined. This review discusses the separation, by chromatography and capillary electrophoresis, and detection, by absorbance, fluorescence, electrochemistry, and immunoassay techniques. When separation pre-concentration is accompanied by laser-induced fluorescence or biuret-based electrochemical detection, nM-pM detection limits are obtained.