CORRELATION BETWEEN CHROMATOGRAPHIC AND PHYSICOCHEMICAL PROPERTIES OFSTATIONARY PHASES IN HPLC - C-30 BONDED REVERSED-PHASE SILICA

In comparison to conventional C-18 phases, C-30 phases exhibit superio r shape selectivity for the separation of isomers of carotenoids and v itamins. To obtain this enhanced recognition capability the HPLC separ ation must be performed at a well-defined temperature. At higher tempe ratures the capability of differentiating between different stereochem ical isomers is lost, resulting in peak coelution, This separation beh aviour is primarily dependent upon the organisation of the C-30 alkyl chains on the silica surface which can be visualised as two domains, t he more ordered domain containing relatively rigid n-alkyl groups with trans conformations and the less ordered environment containing more flexible n-alkyl groups with gauche conformations. The ratio between t rans vs. gauche conformations of the n-alkyl groups directs the shape selectivity of the C-30 phase. The temperature-dependent interconversi on of trans to gauche conformations can be monitored by temperature-de pendent solid-state nuclear magnetic resonance (NMR) and suspended-sta te NMR measurements and visualised by molecular modelling calculations . Thus a direct correlation between chromatographic and physicochemica l properties of C30 bonded phases is possible. (C) 1998 Published by E lsevier Science B.V. All rights reserved.