INFLUENCE OF THE MODIFIERS ON THE NATURE OF THE STATIONARY PHASE AND THE SEPARATION OF CAROTENES IN SUBCRITICAL FLUID CHROMATOGRAPHY

Sixteen solvents were tested as modifiers in the separation of alpha- and beta-trans/cis carotenes by sub-critical fluid chromatography. The results obtained indicate that the retention behaviour is related to solubility parameters and the dielectric constant of the solvents. The study of the selectivity of the trans/cis isomers of beta-carotene leads to a better understanding of the role of the solvents in determining the nature of the stationary phase at the mobile phase interface. The results obtained point out the difference in the conformation of the alkyl chains with three classes of solvents: methanol, acetonitrile, and THF or methylene chloride. The analogy between non aqueous reversed-phase chromatography (NARP) and sub-critical fluid chromatography has also been discussed.