Pirkle-type phases

There is a wide variety of commercially available chiral stationary phases and mobile phase additives.32 34 Preparative scale separations have been performed on the gram scale.32 Many stationary phases are based on chiral polymers such as cellulose or methacrylate, proteins such as human serum albumin or acid glycoprotein, Pirkle-type phases (often based on amino acids), or cyclodextrins. A typical application of a Pirkle phase column was the use of a N-(3,5-dinitrobenzyl)-a-amino phosphonate to synthesize several functionalized chiral stationary phases to separate enantiomers of... 

Pirkle-type phases are amino acid derivatives possessing an aromatic entity which can undergo n-n interactions with the solute. The aromatic entity can be either a n donor or n acceptor. The CSP and the solute form a n donor/acceptor pair. This complex is then stabilized by additional interactions such as hydrogen bonding, dipole interactions, or steric repulsion [8]. The Pirkle-type phases are most commonly used in normal-phase mode in order to enhance the n-n and hydrogen bond interactions. Hexane with an alcoholic modifier, such as isopropanol, is the mobile phase of choice. These phases have... 

The optimization of enantiomer separations follows a similar approach as shovm in Table 6. Under normal-phase conditions, Pirkle-type phases require an apolar base solvent , which is modified in terms of its elution strength by adding one or more additives. For example, if at the selected solvent composition the analyte elutes within the dead time, the amount of polar additive must be reduced, e.g. from 50% to 25%. If under these conditions no partial separation can be observed, it is recommended to change to another Pirkle phase. 

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