Separation of Tocopherol Isomers Using Capillary Electrochromatography:  Comparison of Monomeric and Polymeric C₃₀ Stationary Phases

Abstract

The comparison of tocopherol isomer separation achieved using different stationary-phase alkyl chain lengths (i.e., C18 vs C30) and modes of alkyl phase attachment to the silica-based supports (i.e., polymeric vs monomeric synthesis) using capillary electrochromatography (CEC) has been demonstrated. The smaller alkyl chain does not exhibit the shape selectivity needed to resolve all of the tocopherol isomers. Conversely, both polymeric and monomeric C30 phases show increased tocopherol isomer selectivity. Changing the elutropic strength of the mobile phase had dramatic effects on the selectivity, with small additions of water to a methanol mobile phase yielding the best selectivity. The complete baseline separation of the tocopherol isomers was achieved using the monomerically bound C30 stationary phase and a methanol/ water mobile phase. The differences in stationary-phase selectivity were examined using a NIST standard reference material for determining column selectivity in LC. The results indicated that the monomeric C30 actually had "intermediate" phase characteristics (i.e., high phase loading, end capping, etc). This new CEC-based separation was also used to separate the tocopherols in a vitamin E supplement sample.

Determination of tocopherols in vegetable oils by CEC using methacrylate ester‐based monolithic columns

“…Using CEC, compounds with closely similar properties can be resolved in a short time with minimal solvent consumption. The separation of vitamin E components by CEC using packed columns has been described [20][21][22][23][24][25]. Quantitation studies of these compounds in edible oils with a CEC-packed column have been reported [24], but application to detect oil adulteration was not demonstrated.…”

Rapid assay of vitamin E in vegetable oils by reversed‐phase capillary electrochromatography

“…The analysis of TOHs was optimized using two miniaturized techniques, namely capillary electrochromatography (CEC) [17][18][19][20] and nano-liquid chromatography (nano-LC) [21]. CEC is a hybrid technique combining aspects of both HPLC and CE.…”

Recent applications in capillary electrochromatography

“…This method was applied for the qualitative analysis of vitamin E in human serum extracts. Henry et al [102] investigated several RP-stationary phases for the separation of tocopherol a-, b-, g-, and d-isomers. Using a C 30 monolithic stationary phase, the effect of the eluent composition was systematically studied.…”

“…Effect of the addition of 1% water to the methanol mobile phase on the separation between b-, g-tocopherol isomers using a C 30 monolithic stationary phase. Reprinted from [102], with permission.…”