Prediction of GC retention values under various column temperature conditions from temperature programmed data

A numerical approach has been developed for the correlation of retention limes (total retention lime) with temperature in gas chromatography, which allows the calculation of retention parameters including retention index from data acquired under two or more different temperature program conditions. By using this procedure the optimization of temperature condition can be further achieved, especially when a temperature-programmed run is the most suitable mode in the preliminary development of an analytical method for the analysis of an unknown sample.

Characteristics of elution profile in radial chromatography under linear conditions

Based on the mass balance equations of solute transfer in the radial chromatographic column, the theoretical expression to describe the column efficiency and shape of elution profile is obtained under linear isotherm case. Moreover, the tendency for the variation of column efficiency and symmetry of peak profile is systematically discussed. The results showed that in radial chromatography the relationship between the column efficiency and volumetric flow rate is similar with that relationship in axial chromatography; relatively high column efficiency still can be obtained under high flow rate in radial chromatography. Accompanying the increase of retention factor of solutes and injection time, the column efficiency decreases monotonously. The effect of column diameter and column length on the column efficiency interfere with each other. It is more advantageous to increase the column efficiency by applying columns with larger column diameter and shorter column length. According to the discussion of the effect of diffusion on the column efficiency, radial chromatography is proved to be suitable for the separation of samples with relatively high diffusion coefficient, which predicts its obvious advantage in the preparative separation of samples such as proteins and DNA.

Highly ordered periodic mesoporous ethanesilica synthesized under neutral conditions

Highly ordered mesoporous ethanesilica (MES) with 2D hexagonal structure was synthesized from 1,2-bis(trimethoxysilyl) ethane under neutral conditions for the first time. Divalent salts, such as NiCl2, MgCl2, ZnCl2, ZnSO4 and Zn(NO3)(2), were used to help the formation of the ordered mesostructure. The MES samples were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, FT-IR, C-13 and Si-29 solid-state NMR and thermal gravimetric analysis. A phase transition from a disordered wormhole-like structure to an ordered P6mm structure was observed upon the addition of inorganic salts. The pore size of the MES decreases from 4.7 to 3.9 nm with increasing content of the inorganic salts. Fluoride was also found to be important for the formation of ordered MES under neutral conditions.

Direct synthesis of highly ordered Fe-SBA-15 mesoporous materials under weak acidic conditions

Iron-substituted SBA-15 (Fe-SBA-15) materials have been synthesized via a simple direct hydrothermal method under weak acidic conditions. The powder X-ray diffraction (XRD), NZ sorption and transmission electron microscopy (TEM) characterizations show that the resultant materials have well-ordered hexagonal meso-structures. The diffused reflectance UV-vis and UV resonance Raman spectroscopy characterizations show that most of the iron ions exist as isolated framework species for calcined materials when the Fe/Si molar ratios are below 0.01 in the gel. The presence of iron species also has significant salt effects that can greatly improve the ordering of the mesoporous structure. Different iron species including isolated framework iron species, extraframework iron clusters and iron oxides are formed selectively by adjusting the pH values of the synthesis solutions and Fe/Si molar ratios. (c) 2005 Elsevier Inc. All rights reserved.

Complete hydrodechlorination of chlorobenzene and its derivatives over supported nickel catalysts under liquid phase conditions

Liquid phase hydrodechlorination of chlorobenzene was studied over Ni/active carbon (Ni/AC), Ni/gamma-Al2O3, Ni/SiO2 and Raney Ni. The complete hydrodechlorination of chlorobenzene was realized at 333-343 K on Ni/AC under hydrogen atmosphere of 1.0 MPa in the presence of alkaline hydroxide. Aryl halides, three chlorotoluenes (o-, m- and p-), three chloroanilines, three chlorobenzotrifluorides, three dichlorobenzenes and two trichlorobenzenes (1,2,3- and 1,2,4-) were also completely hydrodechlorinated under the similar conditions. Chlorobenzene derivatives having either an electron-donating group or an electron-withdrawing group decreased their reactivities with respect to the unsubstituted chlorobenzene.