Stationary phases alumina/silica

Substituted monocyclic phenols have been widely studied on several stationary phases (alumina, silica gel, cellulose, polyamide, silanized silica gel) and also on chemically modified adsorbents (cyano- and amino-silica plates), ion-exchange layers, and impregnated plates. 

A wide variety of organic compounds have been subjected to D-TLC. Among others, corticosteroids, ecdysteroids, morphine and its semisynthetic derivatives and various phenylalkylamines have been displaced using planar stationary pha.ses. The material of the stationary phase was silica, alumina and reversed-phase (Cix) silica. 

In thin-layer chromatography cellulose can also be put in as a stationary phase Alumina and silica geP " and mfactures... 

Calculate how much of the stationary phase (alumina or silica) is required by assessing the optimum... 

If the analytes are very polar and neutral, the best analytical technique is likely to be hydrophilic interaction chromatography. It has proved its value for the analysis of carbohydrates. Hydrophilic interaction chromatography is carried out using very polar stationary phases in conjunction with aqueous mobile phases with a high organic content. Useful stationary phases are silica, alumina, polar bonded phases such as aminopropyl or diol, and even ion exchangers. The stability of the aminopropyl bonded phase in aqueous eluents is limited, but the other stationary phases can be recommended without reservation. For a detailed discussion, see Chapter 11. 

Stationary phases of silica gel are most often used but alumina is a suitable alternative. A wide range of development solvents have been reported, many of which use chemicals (benzene, chloroform) considered undesirable today on account of their toxic properties. Mixtures of solvents are invariably required, such as chloroform/methanol benzene/chloroform/ethanol ethyl acetate/dimethyl-formamide/ethanol benzene/acetone/diethyl ether chloroform/acetone/acetic acid and chloroform/ethanol. 

The unmodified stationary phases include silicas, aluminas. Kieselguhr, silicates, controlled-po-rosity glass, cellulose, starch, gypsum, polyamides, and chitin. For TLC and HPTLC the most... 

Stationary phases SI silica gel, CN cyanopropyl silica, AM amino-bonded silica. DIOL diol-bonded silica, C-2 dimethyl silica. C-8 octyl silica, C-18 octadecyl silica, Ce cellulose. AL alumina, Po polyamide coated silica, I-P impregnated with paraffin. I-F impregnated with formamide, I-Ag impregnated with silver nitrate, 1-Pg impregnated with propylene glycol. 

In LPLC, a mobile phase is allowed to flow through a densely packed sorbent. The separation mechanism is adsorption or size-exclusion depending on the choice of packing material for the stationary phase (adsorption silica gel, bonded-phase silica gel, alumina, polystyrene size-exclusion polyacrylamide, carbohydrates). This is almost similar to... 

In liquid-solid adsorption chromatography (LSC) the column packing also serves as the stationary phase. In Tswett s original work the stationary phase was finely divided CaCOa, but modern columns employ porous 3-10-)J,m particles of silica or alumina. Since the stationary phase is polar, the mobile phase is usually a nonpolar or moderately polar solvent. Typical mobile phases include hexane, isooctane, and methylene chloride. The usual order of elution, from shorter to longer retention times, is... 

An important publication by Kost et al. (63JGU525) on thin-layer chromatography (TLC) of pyrazoles contains a large collection of Rf values for 1 1 mixtures of petroleum ether-chloroform or benzene-chloroform as eluents and alumina as stationary phase. 1,3- and 1,5-disubstituted pyrazoles can be separated and identified by TLC (Rf l,3>i y 1,5). For another publication by the same authors on the chromatographic separation of the aminopyrazoles, see (63JGU2519). A-Unsubstituted pyrazoles move with difficulty and it is necessary to add acetone or methanol to the eluent mixture. Other convenient conditions for AH pyrazoles utilize silica gel and ethyl acetate saturated with water (a pentacyanoamine ferroate ammonium disodium salt solution can be used to visualize the pyrazoles). 

Liquid-solid chromatography (LSC). This process, often termed adsorption chromatography, is based on interactions between the solute and fixed active sites on a finely divided solid adsorbent used as the stationary phase. The adsorbent, which may be packed in a column or spread on a plate, is generally a high surface area, active solid such as alumina, charcoal or silica gel, the last... 

The same concepts apply to column chromatography, where the stationary phase is normally small particles of silica, Si02, or alumina, A1,0 . These substances are not very reactive and have specially prepared surfaces to increase their adsorption ability. The column is saturated with solvent, and a small volume of solution containing the solutes is poured onto the top. As soon as it has soaked in, more solvent is added. The solutes travel slowly down the column and are eluted (removed as fractions) at the bottom (Fig. 2). If the mobile phase is less polar than the stationary phase, the less polar solutes will be eluted first and the more polar ones last. 

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... 

Adsorption and ion exchange chromatography are well-known methods of LC. In adsorption, one frequently selects either silica or alumina as stationary phase for separation of nonionic, moderately polar substances (e.g. alcohols, aromatic heterocycles, etc.). This mode works best in the fractionation of classes of compounds and the resolution of isomeric substances (J). Ion exchange, on the other hand, is applicable to the separation of ionic substances. As to be discussed later, this mode has been well developed as a tool for analysis of urine constituents (8). 

Stationary phase Silica gel, alumina, cellulose Silica gel (mainly), alumina, cellulose... 

The separations of some nonionic tensides having biological activity and consisting of ethyleneoxide oligomer mixtures were performed in many different TEC systems (silica and alumina as the stationary phase and single solvent or binary mixtures as the mobile phase). Selectivity was higher on alumina than on the silica layer. Both... 

Silica gel or alumina is usually used as the stationary phase. For these active phases a solvent of weak elution power is recommended for dissolution of the sample. A... 

This technique is based on the same separation mechanisms as found in liquid chromatography (LC). In LC, the solubility and the functional group interaction of sample, sorbent, and solvent are optimized to effect separation. In SPE, these interactions are optimized to effect retention or elution. Polar stationary phases, such as silica gel, Florisil and alumina, retain compounds with polar functional group (e.g., phenols, humic acids, and amines). A nonpolar organic solvent (e.g. hexane, dichloromethane) is used to remove nonpolar inferences where the target analyte is a polar compound. Conversely, the same nonpolar solvent may be used to elute a nonpolar analyte, leaving polar inferences adsorbed on the column. 

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