Reverse phase chromatography alumina columns

Many forms of chromatography have been used to separate mixtures of quinoline and isoquinoline homologues. For example, alumina saturated with cobalt chloride, reversed-phase Hquid chromatography, and capillary gas chromatography (gc) with deactivated glass columns have all been employed (38,39). 

The stationary phase matrices used in classic column chromatography are spongy materials whose compress-ibihty hmits flow of the mobile phase. High-pressure liquid chromatography (HPLC) employs incompressible silica or alumina microbeads as the stationary phase and pressures of up to a few thousand psi. Incompressible matrices permit both high flow rates and enhanced resolution. HPLC can resolve complex mixtures of Upids or peptides whose properties differ only slightly. Reversed-phase HPLC exploits a hydrophobic stationary phase of... 

Recently, Janjic et al. published some papers [33-36] on the influence of the stationary and mobile phase composition on the solvent strength parameter e° and SP, the system parameter (SP = log xjx, where and denote the mole fractions of the modiher in the stationary and the mobile phase, respectively) in normal phase and reversed-phase column chromatography. They established a linear dependence between SP and the Snyder s solvent strength parameters e° by performing experiments with binary solvent mixtures on silica and alumina layers. 

The removal of sterols, vitamin E vitamers, carotenoids, and other interfering material from the unsaponifiable fraction of food samples has been achieved using one or more of the following techniques coprecipitation of sterols with digitonin (91), precipitation of sterols from a methano-lic solution (195,209), adsorption chromatography on open columns of alumina (70,91,96), thin-layer chromatography on silica plates (209), and solid-phase extraction on silica (68,100) and reversed-phase (210) cartridges. 

Alumina offers another alternative to silica because of its inherent higher pH stabihty. However, in contrast to its extensive use as a medium in column chromatography for purification purposes, or for separations in the normal-phase mode, there are still relatively few reports concerning alumina-based materials in the reversed-phase mode. 

In addition to silica, (Si02)x, alumina, (A1203)V, is amongst the most common adsorbents in liquid solid chromatography. Although highly efficient separator columns were developed in the past with spherical beads of small diameter, this separation material is only of minor importance since the introduction of chemically bonded reversed phases on the basis of silica in HPLC. 

In normal-phase liquid chromatography on silica and alumina the hydrogen bonding of fullerenes with surface hydroxyl groups of adsorbent is the most important. On separation of Ceo and C70 on a column packed by alumina Alusorb N 200 from n hexane the selectivity is 1.80 (Fig. 2 a.). The reversed-phase adsorbents such as silica with bonded diphenylsilyl... 

Normal-phase, bonded-phase columns are likely underutilized for separations where they should be the method of choice. This is due both to the ease of use of reversed-phase, bonded-phase columns, discussed next, and also to the many problems inherent in the use of bare silica and alumina. Very straightforward method development in normal-phase chromatography can be performed by combining the solvent and stationary-phase selectivity triangles. The three columns, each used with the three recommended modifiers, should provide the maximum difference in selectivity available. These nine experiments, used in conjunction with chemometric optimization schemes, should then provide a ratio-... 

Normal phase chromatography is used where very nonpolar molecules take too long to elute from a reversed-phase column. It, too, is based on the principle that Uke dissolves Uke and uses polar columns, e.g. silica or alumina, and nonpolar mobile phases, e.g. toluene or hexane. Molecules distribute themselves between the stationary and mobile phases to different extents depending on factors such as polarity, size and pKa. Large nonpolar molecules will elute first. 

In an effort to uncover anticancer active metabolites in Brazilian plants, in early 1993 we initiated active collaboration with several Brazilian natural products chemists. Out of the large number of extracts brought to our laboratory by Dr. Vanderlan da S. Bolzani and screened in our mechanism-based yeast bioassay, extracts derived from two leguminous plants were selected for further studies. Based on preliminary investigation the bioactive methanolic chloroform extract of the leaves of Cassia leptophylla which was shown to contain bioactive alkaloidal constituents was further processed for alkaloids. The alkaloid fraction thus obtained was fractionated by column chromatography on alumina, followed by Silica gel preparative TLC and reversed-phase TLC to afford seven piperidine alkaloids [55] (-)-spectaline (68), (-)-spectalinine (69), canavaline (70), leptophyllin A (71), 3-acetylleptophyllin A (72), iso-... 

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