Improved crown ether-based chiral stationary phase

Abstract

An improved crown ether-based chiral stationary phase (CSP) was prepared by dynamic coating of a reversed-phase silica gel with a new chiral crown ether which was designed to have more lipophilicity than the previously used one, while preserving the basic structure responsible for chiral recognition. The CSP showed not only excellent enantioselectivity for amino acids, but also higher stability against organic solvents in the mobile phase. No desorption of the crown ether from the support was observed in a mobile phase containing up to 40% of methanol. An increase in methanol concentration in the mobile phase gave rise to a decrease in the retention of amino acids and an increase in the “apparent” enantioselectivity, i.e., the separation coefficient and the resolution factor. A possible retention mechanism is proposed to explain these behaviours.