Describe the types of stationary phases used for chiral separations in HPLC including structural requirements.
The stationary phases for chiral separation can be classified into 5 main types. These types were first proposed by Irving Wainer and are hence also known as the Wainer classification.
Type I - those that differentiate enantiomers by the formation of complexes based on attractive interactions. These may be hydrogen bonds, p-p interactions, dipole stacking. The two main types of stationary phases in this type are pi-acceptor and pi-donor phases. The most common pi-acceptor phase is N-(3,5-dinitrobenzoyl) -phenylglycine bonded to n-propylamino silica. These columns are capable of separating a large range of compounds which include a pi-donor aromatic group.
Type II - those that involve a combination of attractive interactions and inclusion complexes to produce a separation. Most type II phases are based on cellulose derivatives. Columns available include microcrystalline triacetate- (MCTA), tribenzoate-, trisphenylcarbamate- and tris(3,5-dimethylphenylcarbamate)- cellulose. Some of the applications include separations of small aliphatic ...
The solution describes the stationary phases for chiral separations.