Chromatography stationary phase preparation

Another method that is becoming very important is chromatography using a chiral phase. Often, a chiral stationary phase, prepared by covalently bonding a chiral compound to the surface of silica beads, is used. 

Cert, A. and Moreda, W. (1998) New method of stationary phase preparation for silver ion column chromatography application to the isolation of steroidal hydrocarbons in vegetable oils. J. Chromatogr., 823, 291-297. 

There are growing numbers of reports indicating that chiral ionic liquids may be useful in many areas of science and technology, though synthesis and use of chiral ILs is in its infancy. For example, the use of ephedrinium-based chiral ILs (Fig. 5) as a gas chromatography stationary phase has been reported [12], Chiral ILs can be prepared either from chiral starting materials (Scheme lb) or using asymmetric synthesis (Scheme la) [13]. 

Gasparrini, E., Misiti, D., Rompietti, R., Villani, C. New hybrid polymeric liquid chromatography chiral stationary phase prepared by surface-initiated polymerization,/. Chromatogr. A, 2005,1064, 25-38. 

Lai, J.P. Lu, X.Y. Lu, C.Y. Ju, H.F. He, X.W. Preparation and evaluation of molecularly imprinted polymeric microspheres by aqueous suspension polymerization for use as a high-performance hquid chromatography stationary phase. Anal. Chim. Acta. 

Lomsadze K, Jibuti G, Farkas T, Chankvetadze B. Comparative high-performance liquid chromatography enantioseparations using polysaccharide based chiral stationary phases prepared by coating of totally porous and core-shell silica particles. J Chromatogr A 2012 1234 50-55. 

Suedee, R. et al.. Chiral determination of various adrenergic drugs by thin-layer chromatography using molecularly imprinted chiral stationary phases prepared with a-agonists. Analyst, 124, 1003,1999. 

Gas chromatography (gc) is inferior to hplc in separating abiUty. With gc, it is better to use capillary columns and the appHcation is then limited to analysis (67). Resolution by thin layer chromatography or dc is similar to Ic, and chiral stationary phases developed for Ic can be used. However, tic has not been studied as extensively as Ic and gc. Chiral plates for analysis and preparation of micro quantities have been developed (68). 

APPLICATION OF NANOTECHNOLOGY FOR PREPARATION OF STATIONARY PHASE FOR CHROMATOGRAPHY... 

Synthetic chiral adsorbents are usually prepared by tethering a chiral molecule to a silica surface. The attachment to the silica is through alkylsiloxy bonds. A study which demonstrates the technique reports the resolution of a number of aromatic compoimds on a 1- to 8-g scale. The adsorbent is a silica that has been derivatized with a chiral reagent. Specifically, hydroxyl groups on the silica surface are covalently boimd to a derivative of f -phenylglycine. A medium-pressure chromatography apparatus is used. The racemic mixture is passed through the column, and, when resolution is successful, the separated enantiomers are isolated as completely resolved fiactions. Scheme 2.5 shows some other examples of chiral stationary phases. 

Contemporary development of chromatography theory has tended to concentrate on dispersion in electro-chromatography and the treatment of column overload in preparative columns. Under overload conditions, the adsorption isotherm of the solute with respect to the stationary phase can be grossly nonlinear. One of the prime contributors in this research has been Guiochon and his co-workers, [27-30]. The form of the isotherm must be experimentally determined and, from the equilibrium data, and by the use of appropriate computer programs, it has been shown possible to calculate the theoretical profile of an overloaded peak. 

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