A long alkyl group like C30 (triacontyl group) has been known to be more suitable than a conventional C18 phase for the separation of hydrophobic structurally related isomers such as vitamin E or vitamin K1. In this study, the separation factor of beta-tocopherol and gamma-tocopherol which were structurally related isomers were evaluated to vary both the pore diameter of the superficially porous silica and the ligand density of the C30 group. Regarding a pore diameter, 12 nm showed the largest separation factor of beta and gamma-tocopherol among 10nm, 12 nm and 16 nm. Regarding ligand density, the higher the ligand density, the larger the separation factor of beta and gamma-tocopherol. However, when a ligand density was too high, much high hydrophobicity caused peak tailing and a drop of the theoretical plate. The most suitable ligand density existed for the highest resolution. Finally, the separation of cis and trans-vitamin K1 was compared and the same result as the separation of beta and gamma-tocopherol was obtained.
Conclusion *C30 phase could separate β-tocopherol and γ-tocopherol although C18 the phase could not separate such isomers.
The higher the C30 ligand density, the larger the separation factor of β-tocopherol and γ-tocopherol. However, high hydrophobicity on the particle surface made the packing state bad. As a result, more than 2 μmol/m2 of ligand density caused a low theoretical plate and a tailing peak.
C30 phase bonded inside a pore with a 12 nm diameter showed not only high ligand density per volume but also not too high hydrophobicity on the particle surface in order to perform good separation (high theoretical plate and no tailing). Proposed C30 phase (batch# 230216) showed better separation of vitamin K1 isomers than company C C30.