Chemically Bonded Silica Stationary Phases: Synthesis, Physicochemical Characterization, and Molecular Mechanism of Reversed-Phase HPLC Retention

Abstract

Two types of chemically bonded phases for high-performance liquid chromatography (HPLC) have been prepared: a conventional C18 and AP (N-acylaminopropylsilica), a novel one that contains specific interaction sites localized in the hydrophobic chain. Surface properties of stationary phases, before and after chemical modification, have been characterized by several physicochemical techniques, such as porosimetry, ICP atomic emission spectroscopy, elemental analysis, solid state CP/MAS NMR, and chromatography. For the studies of the reversed-phase HPLC retention mechanism under hydroorganic conditions, a test series of structurally diverse solutes has been selected. Sets of retention parameters and structural descriptors of the test solutes were subjected to multiparameter regression analysis. The quantitative structure−retention relationships derived demonstrated the typical reversed-phase partition mechanism to predominate in the separation on the C18 phases but not on the AP phases. The AP phases were demonstrated to provide significant input to retention due to the structurally specific dipole−dipole and charge transfer interactions with the solutes. The proposed AP phases for HPLC possess distinctive and interesting retentive properties, and chemometric analysis of retention data of appropriately designed series of test solutes appears to be a convenient, objective, and quantitative method to prove a new phase specificity.