Highly efficient separation of amines by electrokinetic chromatography using resorcarene-octacarboxylic acids as pseudostationary phases

Abstract

Resorcarene-octacarboxylic acids, macrocyclic molecules built up by four alkylidene-bridged resorcinol units, were synthesized and used as pseudostationary phases in electrokinetic chromatography (EKC). Resorcarenes provide a stable structure and good solubility in electrolytes even with organic modifiers. The high electrophoretic mobility of the resorcarene-octacarboxylic acids introduced here as pseudostationary phases is based on the eight partly deprotonated carboxylic groups. This offers a broad migration time window, which is the main parameter for the resolution of peaks. From three compounds with different alkyl chain lengths (C1, C5, C11), the C11-resorcarene-octa-acid possesses an extremely high selectivity for lipophilic compounds which is demonstrated by the efficient separation of thirteen homologous or isomeric amines derivatized with o-phthaldialdehyde and 2-mercaptoethanol. The order of peak elution is almost identical with that known in reversed-phase high performance liquid chromatography. Sensitive detection of amines is achieved using laser-induced fluorescence. Efficiencies up to 3 million plates/m were obtained resulting from the small detection window based on the intense focusing of the laser beam, a sample focusing effect in the sample zone and the absence of electrophoretic microheterogeneity of the pseudostationary phase.