Specialty columns chiral stationary phases

Preparative chromatography is a proven technology for the separation of specialty chemicals mainly in food and pharmaceutical industries, particularly the enantioseparation of chiral compounds on chiral stationary phases. The potential of preparative chromatographic systems were further increased by the development of continuous chromatographic processes like the simulated moving bed (SMB) process. Compared to the batch column chromatography, the SMB process offers better performance in terms of productivity and solvent consumption [2]. 

Some of the more popular ones are phases with shorter alkyl chains such as Cs (8 carbons) or C4 (4 carbons). Specialized columns with chiral stationary phase are also available for the separation of enantiomers (mirror image isomers). Bonded stationary phases, which are polar, also exist common ones are cyano, phenyl, and amino columns, which have respectively GN, phenyl, and NH2 groups bonded to the silica support via short alkyl linker chains. These latter columns as well as HPLG columns packed with unbonded silica all have specialty uses but it is estimated approximately 80% of all HPLG separations are done using some form of reversed-phase, most commonly Gig because of its versatility and reproducibility. 

For the separation of chiral molecules into their respective enantiomers, several approaches are possible by HPLC. These include precolumn derivatization to form diastereomers, followed by the use of normal-phase or reversed-phase HPLC, or addition of the derivatization reagent to the chromatographic mobile phase to form dynamic diastereomers during the separation process. Alternatively, specialty columns prepared with cyclodextrins or specific chiral moieties as stationary phases may be used. 

Two types of stationary phases are most popular the polysiloxanes and polyethylene glycol phases. Both types of phases may be characterized as having the necessary high viscosity and the capability for crosslinking and/or chemical bonding with fused silica. One should note the presence of more recent additions to the capillary column family, namely, specialty columns designed for selected EPA methods, chiral separations, and gas-solid chromatographic separations. These specialty phases are considered in Section 3.11.6. 

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