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
Stationary phase design and characterization have been central to the development of liquid chromatography. With fundamental knowledge of retention mechanisms it is possible to tune selectivity and optimize the separation of different classes of compounds. Among the factors that can influence selectivity are bonded phase length and bonding chemistry. Although numerous efforts have been made to examine the effect of chain length on retention behavior in reversed phase liquid chromatography, surprisingly, odd chain length stationary phases have yet to be studied.
Six different alkyl chain lengths, ranging from C13 to C18, were prepared for study. Monomeric, polymeric, and self-assembled monolayer phases were synthesized for each of the alkyl chain lengths. All of the phases were synthesized on the same lot of silica, minimizing the effect of the substrate configuration. Methylene selectivity was tested with a homologous series of alkyl benzenes and shape selectivity was probed at a series of temperatures with Column Selectivity Test Mixture for Liquid Chromatography, Standard Reference Material (SRM) 869a. A comparison of the effects of varying chain length, bonding chemistry, and temperature will be presented.