Evaluation of Long Chain Stationary Phase Selectivity  for Measurement Problems

Catherine Rimmer, Lane C. Sander, and Stephen A. Wise

Analytical Chemistry Division, Chemical Sciences and Technology Laboratory
National Institute of Standards and Technology, Gaithersburg, MD 20899-8392

The potential health benefits associated with carotenoids have driven interest in their separation, identification and quantitation.  These highly conjugated molecules have provided a significant separation challenge, as they exist as a complex series of positional and geometric isomers.  In liquid chromatography (LC) the separation of carotenoid isomers is dependent on many factors including the length and density of the alkyl bonded phase.

Previous work in our laboratory resulted in the design of the polymeric C30 phase specifically for the separation of carotenoids.  The C30 phases are comparable in length to the molecules of interest; as a result they exhibit enhanced selectivity.  Recently, a longer phase has been synthesized.  Poly(ethylene-co-acrylic acid) (PEAA) has been immobilized on chromatographic silica through a covalent bond with a glycidoxypropyl or aminopropyl linkage.  When the PEAA has a 5% mass fraction of acrylic acid, the length of the resulting bonded phase is roughly equivalent to a C100 alkyl phase.

Standard Reference Material (SRM) 869a Column Selectivity Test Mixture for Liquid Chromatography, SRM 870 Column Performance Test Mixture for Liquid Chromatography, SRM 1647d Priority Pollutant Polycyclic Aromatic Hydrocarbons, isomerized alpha-carotene, isomerized beta-carotene, and a mixture of alpha, beta, gamma, and delta tocopherol have been used for the characterization of commercially available C30 columns and several PEAA columns.  The differences in retention and selectivity will be discussed.