On the mechanism of carotenoid separation in "monomeric" reversed phases
DOI:
https://doi.org/10.17308/sorpchrom.2026.26/13691Keywords:
RP HPLC, lutein diesters, dead volume, retention mechanismAbstract
The chromatographic behavior of xanthophyll diesters in reverse-phase chromatography on "monomeric" reversed phases is studied. A choice of solvents for the composition of mobile phases is proposed based on the solubility of xanthophyll diesters in them and other special properties of the solvents. The elution forces of mobile phases in which acetone, propanol-2, ethyl acetate, methylene chloride, and methyl tert-butyl ether are used in a mixture with acetonitrile are compared. The choice of the "ethyl acetate – acetonitrile" system in this work is justified. The features of determining the dead time of a chromatographic system using homologous series, which include xanthophyll diesters and uracil, are considered, and the use of chlorogenic acid as a substance with a larger size compared to uracil is proposed to reduce the exclusion effects. It is shown that the first option has disadvantages, since the results of determining the dead time depend on the length of the radicals in the test compounds, but when used in the first three pairs of homologues, data is obtained that is almost equal to the results of the third option, which confirms the importance of exclusive effects and determines the choice of the main method for subsequent studies. A comparison of the retention factors of xanthophyll diesters is proposed when replacing stationary phases of the same brand based on identical silica gels, but with different lengths of grafted alkyl groups: C18 and C8. It is shown that new ideas on the structure of silica gel are taken into account as a product of coagulation of non-porous nanoparticles of silica sol, leading to a convex shape of the sorption surface inside the silica gel microparticles. In this case, the model of the grafted layer structure is replaced by a similar model with a fan-shaped arrangement of alkyl radicals, which dramatically increases the volume of voids between the grafted radicals and the difference in the volume of voids (filled with mobile phase components) in phases C8 and C18, which confirms the distributional mechanism of sorption of xanthophyll diesters in the "monomeric" reversed phases. Finally, the high probability of the dominance of this mechanism is confirmed by the consistency between the logarithms of retention factors and lipophilicity (as ClogP) of some carotenes.
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