Classification of LC chiral stationary phases: Wainer Types I–V revisited

•Importance of Wainer classification in early chiral LC development highlighted.•Justification of importance of classifying chiral LC stationary phases made.•Alternatives for LC chiral stationary phase classification considered.•Attention drawn to relevance of Wainer classification in single enantiomer drug patent Litigation.•Justification made for continuing value of Wainer classification to modern day chiral LC.

The method of classifying LC chiral stationary phases (CSPs) introduced by Irving Wainer in 1987 became widely adopted largely because it was based on the mechanisms by which the different CSP Types (I–V) achieved chiral recognition and was an integral part of a ‘how to do chiral LC’ package. The classification became less used perhaps because it was thought that it was not clear to which Type some of the newer CSPs should be assigned. Its only modern day significance seemed to be in single enantiomer drug patent litigation cases in defining the ‘state-of-the-art’ of chiral LC in the late 1980s. However, on closer inspection, it is clear that even with the introduction of many new commercially available CSPs, the Wainer classification, perhaps with minor modifications, remains a useful suitable vehicle for distinguishing between different groups (Types) of CSPs as an aid to chiral LC method development.