摘要:

Silylated silica surfaces have found many applications in the field of analytical chemistry (HPLC, Ion Exchange Chromatography, Size Exclusion Chromatography, GC), synthetic chemistry (heterogeneous catalysts, phase transfer catalysts), biochemistry (enzyme immobilization, affinity chromatography) and industries (composites, high-tech materials, semiconductor devices).

ISSN:1082-6076    

DOI:10.1080/10826079608015107

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Ethoxysilanes are of growing interest in the fields of immobilized catalysts and chromatography. In spite of this, the reactions of ethoxysilanes with silica surfaces are still not fully explored. This contribution demonstrates that besides the reaction temperature and the degree of dryness of the silica surface, the solvent plays a crucial role during the silanization step: Optimal surface coverage can. for example, be obtained either without solvent or with hydrocarbons likeiso-octane or pentane under mild reaction conditions. Hereby,13C and29Si solid-state NMR spectroscopy serves as a powerful analytical method. The modified silica can be successfully applied for the purification of bifunctional phosphines and their carbonylnickel complexes.

ISSN:1082-6076    

DOI:10.1080/10826079608015108

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Adsorption-desorption isotherms were measured for selected chromatographic silica gels with chemically bonded octyl groups. The standard sorption characterization of these packings provided the BET specific surface area, the total pore volume and the pore size distribution. Advanced numerical methods based on the density functional theory and the regularization method were used to calculate the pore volume and the adsorption energy distributions. The surface and structural properties of the silicas with chemically bonded octyl phases were compared to those of the original silica gels. The surface coverage of octyl groups occurred to be similar for all samples studied. After the octyl groups were bonded, the porous structure of the silica gels was not altered significantly, resulting in similar adsorption behavior of both unmodified and modified silica gels at pressures close to the saturation pressure. However, the adsorption properties in low pressure region were changed significantly. Namely, all modified silicas exhibited very low adsorption and similar shape of adsorption isotherms at low pressures. Therefore, their adsorption energy distributions resembled each other and did not feature the higher energy sites present on the surface of unmodified silicas. The low pressure adsorption behavior indicates that essentially all higher energy sites on the silica surface reacted in the course of the chemical modification.

ISSN:1082-6076    

DOI:10.1080/10826079608015109

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The purity of alkylnitrile compounds has been investigated using gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). The investigation was carried out to supplement earlier reported work using the alkylnitrile compounds, hexanenitrile and valeronitrile, as mobile phase additives in HPLC. GC impurity profiling and GC-MS experiments showed the presence of low level nitrogenous impurities in the alkylnitrile compounds. Analytical interrogation and chemical isolation were employed to identify the impurities as alkylamines. Tri-n-butylamine (TBA) and di-n-pentylamine (DPA) impurities were found in batches of hexanenitrile and valeronitrile respectively and it was found that it was the amine impurities, at very low levels, which caused the observed chromatographic improvements for basic solutes when using the alkylnitrile compounds as mobile phase additives in reversed-phase HPLC. The amines themselves were subsequently used at extremely low levels (ppm) in the mobile phase and were found to be very effective in their action.

ISSN:1082-6076    

DOI:10.1080/10826079608015110

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The horizontal polymerization of trichlorosilanes on silica is discussed with regard to its use in chromatographic separations to reduce silanol activity and improve hydrolytic stability. It is shown that the use of C1spacers, which were previously demonstrated to provide very low silanol activity, are resistant to a pH 10 solution for at least 36 hr. It is also shown that the adsorptivity of water by silica gel is an important factor in achieving dense horizontal polymerization.

ISSN:1082-6076    

DOI:10.1080/10826079608015111

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A thermodynamic equation is used to analyze the retention behavior of phenolic solutes at low modifier concentrations on alkenyl and diol chemically modified silica packings. These materials were prepared by attaching alkenyl and diol ligands with four, six, eight and ten carbon atoms to the surface of LiChrosorb Si-60 silica. The thermodynamic analysis of the capacity ratios of various phenolic solutes measured at different concentrations of simple aliphatic alkohols (used as modifiers) in n-hexane have provided information about solute and solvent interactions with the alkenyl and diol modified silicas. This analysis shows that the solute-alcohol competitive interaction for the alkenyl bonded phases changes significantly with chain length, whereas this effect is not observed for the diol phases. Also, the influence of polarity and geometric structure of functional groups on solute retention have been examined.

ISSN:1082-6076    

DOI:10.1080/10826079608015112

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The effects of pH and ionic strength of the mobile phase, as well as the concentration of organic modifiers, on the retention and elution order of zwitterionic and neutral compounds related to imidazolinone herbicides was studied by using polymeric alkylamide stationary phases. It is shown that retention of these compounds on alkylamide phases is governed by a mixed ionexchange and partition-displacement mechanism. After adjusting pH, ionic strength and composition of the eluent, these phases allow a simultaneous separation of nonpolar and ionic compounds.

ISSN:1082-6076    

DOI:10.1080/10826079608015113

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The chemical modification method based on the silanization of an oxide surface to a hydride intermediate followed by hydrosilation with an organic molecule containing a terminal olefin is reviewed. The resulting bonded organic moiety is attached to the surface via a direct Si-C bond which leads to high stability. The method has been more extensively applied to silica surfaces for the production of stationary phases in HPLC but it can also be used on other oxides such as alumina, zirconia, titania and thoria. More recent applications have been in the modification of the inner wall of fused silica capillaries for HPCE. The bonded moieties possess high stability and useful applications have been developed for the separation of proteins and peptides under a variety of buffer conditions. The same procedure for modifying the inner wall of a fused silica capillary has also been extended to etched surfaces for use in electrochromatography (CEC). This type of CEC has been shown to be applicable to the separation of macromolecules as well as small solutes.

ISSN:1082-6076    

DOI:10.1080/10826079608015114

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The application of a column packing material, 3-(l,8-naphthalimido)propyl-modified silyl silica gel (NAIP) developed by us, for high performance liquid chromatography (HPLC) of barbiturates and diastereomeric compounds is described. The separation of barbiturates by using an NAIP column as a stationary phase was at first investigated. Six commercially available barbiturates (Barbital, Phenobarbital, Amobarbital, Pentobarbital, Secobarbital and Thiopental) were well separated on an NAIP column by an isocratic elution with borate buffer (pH 7.0)-acetonitrile (9:1, v/v). Further, the applicability of the HPLC system including an NAIP column to the determination of barbiturates in human blood plasma was examined. Barbiturates extracted from plasma sample using a solvent extraction (hexane-diethyl ether, 3:7. v/v) were subjected to the HPLC system and determined by an internal standard method with UV detection at 220 nm. The recoveries of barbiturates spiked to human plasma were obtained in the range of 88.6 to 100.0%. The lower detection limits of barbiturates spiked ranged from 0.05 to 0.33 fig/mL, and the within-day and day-to-day precisions for plasma sample (n=5) gave relative standard deviations of less than 9 07% and 18.68%, respectively.

ISSN:1082-6076    

DOI:10.1080/10826079608015115

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Retention behaviors of various planar and non-planar polycyclic aromatic hydrocarbons (PAHs), and all carbon compounds so-called fullerenes with 2,4,6-(tri-tert-butylphenoxy)dimethyl (TBP) silica phase and benzyldimethyl (Benzyl) silica phase have been investigated using microcolumn liquid chromatography system. The results clearly indicate that these phases possess a “non-planarity” recognition capability of PAHs. Non-planar solutes were retained longer than planar ones with these phases under certain separation conditions, although the opposite trend where the planar solutes are retained longer than the non-planar ones was observed with typical octadecylsilica (ODS) phases. This unique behavior can be explained by the specific molecular-molecular interaction between non-planar solutes and the stationary phase moiety having a cavity like structure made by the three tert-butyls and phenyl ring of the moiety. The separation of C60and C70were also examined and the difference of the structural uniqueness between TBP phase and Benzyl phase showed interesting results for such bulky fullerenes separation.

ISSN:1082-6076    

DOI:10.1080/10826079608015116

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor