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Types of Bonded Phase There are three basic types of bonded phases, the brush phases, the bulk phases and the oligomeric phases. The different phases are produced by the use of the mono, di- and tri- substituted silanes respectively in the bonding process, e.g. the monochloro, dichloro and tricoloro silanes. The monochlorosilanes, for instance octyldimethyl-chlorosilane, react with the hydroxyl groups on the silica surface to produce dimethyloctylsilyl chains attached to the silica. Brush Phases The alkyl chains are thought to stand out from the surface like bristles of a brush,

procedure can be used as that in the synthesis of oligomeric phases and the material can be alternatively treated with water and the trichlorosilane reagent. Layers of bonded phase are built up on the surface but, in this case, due to the tricoloro function of the reagent, extensive cross-linking occurs. As a result of the polymerization process, the stationary phase has a chemically cross-linked, multi-layer character and, consequently, is termed a "bulk" phase. The "bulk" phases are almost as popular as the "brush" phases as they tend to have a higher carbon content (more organic material bonded to the surface) and thus provide a little greater retention and selectivity. "Bulk" phases have about the same stability to aqueous solvents and pH as the "brush" phases.   Using appropriate organic chlorosilanes, polar or polarizable groups such as nitriles or aromatic rings can be bonded to the silica to provide stationary phases

of entry and consequently the proximity of interaction which, in turn, will determine the energy of interaction and the magnitude of the retention. Finally, the fifth group contains the cyclodextrin based materials that control retention in a similar manner to that previously described for GC. In LC, the cyclodextrin stationary phases are bonded to a support such as silica and are prepared using similar techniques to those for making reverse phases. The more recent and most effective stationary phases are without doubt those based on the macrocyclic glycopeptides and the cyclodextrins

Liquid Chromatography Stationary Phases Traditionally the stationary phase used in LC has been silica gel which separates solutes largely on the basis of polarity, although, due to its unique structure, silica gel also exhibits strong exclusion characteristics. The bonded phases were introduced to provide a material that would separate solutes by dispersive interactions and also to provide some semie polar stationary phases. The bonded phases were also based on silica gel. More recently, polymeric stationary phases were

Short chain reverse phases reduce the extent to which proteins are denatured in the separation of substances of biological origin, it is seen by the chromatogram from the C2 reverse phase, that a serious price must be paid in loss of resolution if the nature of the separation demands the use of such material. However, the development of the polymer packings have, at last, partly solved this problem. In general, because the brush type phases can be synthesized in a more reproducible manner, particularly if carried out in a fluidized bed, the brush phases are generally recommended for the majority of applications. For high retentive capacity and for systems that will be operated with aqueous solvent mixtures having a very high water content, the bulk phases might be preferred. The partially reacted, low carbon content bulk phase also have special areas of application particularly in sample preparation. Macroporous

Metroprolol respectively and 15 and 20 fm for (S)- and (R)-Atenolol respectively.   The cyclodextrin based stationary phases are some of the more popular and effective chiral stationary phases presently available. One of their distinct advantages lies in their unrestricted and successful use with all types of solvent. In particular, they can be used very effectively in the reversed phase mode (a method of development that is not possible with some other chiral stationary phases) as well as being very effective in a normal phase conditions. They can also be used in the so-called polar organic mode, where the polar constituents of the mobile phase can be anhydrous diethylamine or glacial acetic acid, but in the complete absence of water. The cyclodextrins and their derivatives are widely used for all types of chiral separations, they have a good sample capacity, and can often be used for preparative separations. Cyclodextrin-based phases are readily