Poly(ethylene-co-acrylic acid) stationary phases for the separation of shape constrained isomers

A new approach for the synthesis of long alkyl chain length stationary phas es for use in reversed-phase liquid chromatography is described. Poly(ethyl ene-co-acrylic acid) copolymers (i.e., (-CH2CH2-)(x)[CH2CH(CO2H)-](y)) with different levels of acrylic acid were covalently bonded to silica via glyc idoxypropyl or aminopropyl linkages. C-13 cross polarization magic angle sp inning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy was used to c haracterize the new reversed-phase materials. Aspects of shape selectivity were evaluated for six different columns with Standard Reference Material ( SRM) 869a, Column Selectivity Test Mixture for liquid Chromatography, Selec tivity for isomer separations was enhanced for stationary phases prepared w ith poly(ethylene-co-acrylic acid) containing a mass fraction of 5% acrylic acid. The relationship between alkyl conformation and chromatographic prop erties was studied by C-13 magic angle spinning (MAS) NMR measurements, and correlations were made with the composition of the polymer. Finally, the e ffectiveness of this phase is demonstrated by the separation of several bet a -carotene isomers.