Alumina stationary phases

The parameters of equations describing the dependence of the retention on the concentration of the organic modifier on an alumina stationary phase are compiled in Table 2.42. The coefficient of corrleation varied between 0.816 and 0.999. 

As already discussed, chromatography on silica or alumina stationary phases nowadays should be restricted to the separations of organic soluble compounds. Of course, also ionic and other water-soluble substances have been and will be separated with such phases. But in order to obtain highly efficient separations (i.e., elution of solutes without tailing) the eluent composition has to be selected and adjusted carefully. Such polar components are better separated by applying tended phases or ion exchange or ion pair chromatography. 

Chromatography on silica and alumina is unique among the liquid chromatographic methods in providing maximum selectivity for tfie separation of isomers. It is no problem to separated m- and p-dibromobenzene (a s 1.8 in pentane) (2) or the three nitroanilines (79) on silica or alumina stationary phases with dichloromethane as eluent. 

According to eqn.(3.72) a higher value of ° will result in a lower value for the capacity factor. It can be concluded from table 3.4 that the solvent strength on silica and alumina stationary phases roughly increases with increasing polarity (6) of the solvent, but that there is no quantitative correlation between these two solvent properties. For example, ethers are much stronger solvents (especially on silica) than can be anticipated on the basis of their solubility parameters. 

The objectives of this article are the enumeration and critical evaluation of the recent results obtained in the assessment of the relationship between the physicochemical characteristics and retention behavior of a wide variety of solutes on alumina stationary phases and the elucidation of the efficacy of various multivariate mathematical-statistical methods for the quantitative description of such relationships. 

The chromatographic aspects of the surface characteristics of alumina stationary phases have not been studied as profoundly as zirconia supports however, the presence of hydroxyl and oxide ions on the surface has been reported. 

Cserhati, T. Forgacs, E. Payer, K. Haber, P. Kaliszan, R. Nasal, A. Quantitative structure-retention relationships in separation mechanism studies on polyethylene-coated silica and alumina stationary phases. LC GC Int. 1998, 11, 240. 

Barnes RK, Boyd RE (1982) The chromatographic extraction and purification of Mo from uranium solutions by use of a silver impregnated alumina stationary phase. Int J Appl Radiat Isot 33 479-481... 

Column chromatography has been employed frequently, using either silica or alumina stationary phases, for isolation of individual anthraquinones. Eluents used for column chromatography usually consist of a series of solvents of increasing polarity. Examples of such separations are found in references (41, 47,119). 

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