Selecting the Right CSP

Generally, strategy 1 is applied first and consists in identifying the CSP providing the best selectivity. Numerous preparative applications which follow fhis approach have been reported. Some tools, such as an electronic data base [82, 83] and user guides are available to help in the choice of the appropriate CSP, but the screening of a few CSPs is still fhe more commonly used approach in practice. There are only rare cases for which the chromatographic separation could be predicted. 

When selecting fhe CSP, attention must also be paid to the mobile phase, which 

There is only one recent report by Blackwell et al. on the investigation of the possible rationalization of such effects for a few chiral stationary phases [86], but the prediction of the influence of the mobile phase on the chiral recognition process clearly remains a challenge. Currently, automated screening devices are usually applied to help to find the optimal mobile phase composition. With the introduction of the new immobilized polysaccharide-based phases, this task has been made even more complicated as they tolerate a much wider range of solvent, which in turn may considerably influence the enantioselectivity of the separation. 

In a few cases, the option of preparing tailor-made CSPs for a particular racemic structure has been applied. For example, we prepared on an empirical basis a particular polysaccharide-based CSP for the separation of the enantiomers of the enantiomers of the LTD4 antagonist iralukast and of the antimalaria agent benflumethol [87]. These two racemic drugs were only poorly resolved on the commercially available polysacharide-based phases whereas an excellent separation was obtained on the carbamate derivative of cellulose obtained from cellulose and 3-chloro-4-methylphe-nylisocyanate. The prepared CSP was also used to perform pharmacokinetic studies. 

On a more rational basis (concept of reciprocity), Pirkle and Welch also developed a particular CSP for the separation of the enantiomers of the analgesic agent naproxen and other nonsteroidal anti-inflammatory drugs (NSAID) [88]. It appeared later that this CSP had a relatively broad application range [89]. 

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