Mixed-Mode Liquid Chromatography on Core Shell Stationary Phases Based on Layer-By-Layer Nanodiamond/Polyamine Architecture

摘要

Background: The use of diamond as a chromatographic stationary phase has been studied for more than 45 years now. Detonation nanodiamonds (DND) have been regularly used to increase the low specific surface area of these non-porous stationary phases. Recently, core-shell particles with multiple layers of polyallylamine (PAAm) and DND have been reported for liquid chromatographic separations and solid phase extractions. However, retention mechanisms and selectivity of such core-shell particles are not well -understood due to their complex architecture. Objective: The objective of this work was to perform a detailed evaluation of the mixed mode behavior of three structural analogues of new nanodiamond (ND)/polyamine based core-shell stationary phases. Method: Particles were composed of a glassy carbon core coated with poly(allylamine) (PAAm) and ND, deposited using a layer-by-layer (LbL) approach, with the outer PAAm layer treated with a mixture of a hydrophobic cross-linker and modifier to introduce C_8/C_(18) functional groups. Three types of the core-shell stationary phases having different shell thicknesses and purity of NDs were investigated. Type II was prepared with fewer PAAm/ND bilayers as compared to Type I, whereas Type III was prepared with a same number of bilayers but with an additionally purified form of ND as compared to Type II. Ion-exchange interactions of the phases were tested with a set of model anionic, cationic and ampholytic analytes at different eluent pHs. The relative degree of anionexchange and hydrophobic interactions was also evaluated using a set of dansylated amino acids (Dns-AAs) at varied mobile phase buffer concentrations and organic solvent contents. Results: Anion-exchange properties were noted for all phases at low pH, with the Type I phase exhibiting stronger retention of anionic analytes due to higher PAAm content in its shell. Typical reversed-phase behaviour was observed for the hydrophobic Dns-AAs (Phe, Ile, Leu, Trp,Val and P