Resorcarenes as pseudostationary phases with selectivity for electrokinetic chromatography

Abstract

Resorcarenes, macrocyclic molecules built up by four alkylidene-bridged resorcinol units, have been studied as new pseudostationary phases in order to develop a different mode of pseudophase and to attain a distinct selectivity for electrokinetic chromatography (EKC). This novel pseudostationary phase has several advantages over traditionally used surfactants in micellar electrokinetic chromatography. First, the stable structure of the cyclic tetramer permits the use of high contents of organic modifiers, i.e., >60% (v/v) acetonitrile, to adjust optimum capacity factors. Second, high electrophoretic mobility of the resorcarenes is based on four negative charges delocalized and stabilized over hydrogen bonds. This supplies a broad elution range, which is a main parameter for resolution of separated peaks. Furthermore, these resorcarenes possess unique selectivity for hydrophobic compounds. The order of peak elution with a test mixture involving 12 polycyclic aromatic hydrocarbons (PAHs) is almost identical with that from reverse-phase high-performance liquid chromatography. The first two terms exclude the contribution of microheterogeneity that decreases the efficiency of EKC when common surfactants are used as pseudophases. The selectivities of resorcarenes with methyl, pentyl, undecyl, and p-chlorophenyl groups at the bridging carbons in separation of PAHs are discussed as a function of these residues