Effect of pressure on the selectivity of polymeric C18 and C30 stationary phases in reversed-phase liquid chromatography. Increased separation of isomeric fatty acid methyl esters, triacylglycerols, and tocopherols at high pressure

Distinction of synthetic dl-α-tocopherol from natural vitamin E (d-α-tocopherol) by reversed-phase liquid chromatography. Enhanced selectivity of a polymeric C18 stationary phase at low temperature and/or at high pressure

“…Two stationary phases, polymeric silica C18 (Inertsil ODS-P) and polymeric C30 (Inertsil C30 S-Select) showed opposite elution orders for  and isomers. The separation with C30 and ODS-P was improved at lower temperature and/or at higher pressure, but was not possible with monomeric C18 phases [8]. C30 stationary phase was generally more effective for  andtocopherol separation than ODS-P phase.…”

“…However, greater effects were observed for rigid, planar polynuclear aromatic hydrocarbons than for bulky, flexible ones, particularly on polymeric ODS phase [8,14] Polymeric ODS phase also resulted in very large pressure effects on the retention of alkyl-type solutes [8]. The enhanced selectivity was observed at high pressure and/or low temperature with the opposite elution orders on C30 and ODS-P for -and -tocopherols in a previous study, indicating the attractive interaction of the solute with the stationary phase [8]. The reversed-phase mode does not always separate the four fundamental forms of tocopherol, but has been employed frequently because of short equilibration times and good reproducibility.…”

“…Solutes were measured at 210 nm with the UV-VIS detector. Temperature was controlled by the column oven in a range between 12. between the column outlet and the detector using zero-dead-volume connectors for high pressure operation, as reported earlier [8]. The pressure indicated is the pressure at the pump head.…”

“…Separation of D-D- D-, and D--tocopherol by HPLC has been reported with normal-phase HPLC using silica, amino, and diol stationary phases [3,4], with reversed-phase HPLC using silica-C30, pentafluorophenyl, high-density C18 stationary phase with polymeric bonding [5,6,7,8], and with monolithic columns possessing a polymer stationary phase [9,10]. Normal phase LC separates all natural tocopherol isomers, and is well suited for direct injection of oils, but is not used for complicated biological samples in practice.…”

“…Some special stationary phases have been employed for the separation of -and -tocopherolsin reversed-phase liquid chromatography [5][6][7][8]. Two stationary phases, polymeric silica C18 (Inertsil ODS-P) and polymeric C30 (Inertsil C30 S-Select) showed opposite elution orders for  and isomers.…”