Evaluation of C30 Phase Bonded on Superficially Porous Silica

Norikazu Nagae, R&D, ChromaNik Technologies Inc., Osaka , Japan

A long alkyl group like C30 (triacontyl group) phase has been known to be more suitable than a conventional C18 phase for separation of hydrophobic structurally related isomers such as vitamin E or vitamin K1. In this study, separation factor of beta-tocopherol and gamma-tocopherol which were structurally related isomers was evaluated to vary both a pore diameter of the superficially porous silica and a 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 a ligand density, the higher a ligand density, the larger a 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 theoretical plate. The most suitable ligand density existed for the highest resolution. Finally separation of cis and transvitamin K1 was compared and the same result as separation of beta and gamma-tocopherol was obtained.

Conclusion

*C30 phase could separate β-tocopherol and γ-tocopherol although C18 phase could not separate such isomers.

* The higher C30 ligand density, the larger separation factor of β-tocopherol and γ-tocopherol. However, high hydrophobicity on the particle surface made 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 12 nm diameter showed not only high ligand density per volume but also no too high hydrophobicity on the particle surface in order to perform good separation (high theoretical plate and no tailing).