Assessment of chiral stationary phases for suitability for combined enantiomeric impurity/related substances assays

Chiral stationary phases (CSP) for LC had a major impact on pharmaceutical R&D when they first became commercially available in the 1980s. Even although the use of CSP in pharmaceutical R&D is now very much a mature area, there is still scope for using CSP more effectively to bring about efficiencies. One such instance is the possibility of combining the chiral LC test for the level of a trace enantiomeric impurity in a chiral drug substance and the LC test for related substances into one test. It was envisaged that this could be achieved by carrying out reversed-phase LC on an ODS silica/CSP coupled column system. In evaluating Chiralpak QD-AX, Cyclobond I 2000 DNP and Whelk-O1 CSP using a polar organic - aqueous mobile phase it was found that the Whelk-O1 CSP had good achiral selectivity, the required match of retentivity with the ODS silica material. ACE 5 C18 and also exhibited an encouraging degree of enantioselectivity in the reversed-phase mode. Following consideration of the selectivity of the ACE 5 C18 and Whelk-O1 phases it became apparent that it might be possible to achieve the desired goal of achieving both the enantiomeric impurity and related substances separations in one system by using the Whelk-O1 CSP on its own. This was subsequently demonstrated to be the case using S-naproxen, laevokalim and S-flurbiprofen as illustrative examples. (C) 2011 Elsevier B.V. All rights reserved.