Preparation and evaluation of a monolithic molecularly imprinted polymer for the chiral separation of neurotransmitters and their analogues by capillary electrochromatography

Abstract

A monolithic molecularly imprinted polymer (MIP) column was prepared as the stationary phase for the capillary electrochromatographic (CEC) separation of a group of structurally related compounds including dopamine (DA), (±)-epinephrine (EP), (−)-isoproterenol (ISO), (±)-norepinephrine (NE), (±)-octopamine (OCT), and (±)-synephrine (SYN). Here, (−)-NE was used as the template. Either methacrylic acid (MAA) or itaconic acid (IA) together with a mixture of ethylene glycol dimethacrylate (EDMA) and α,α′-azobis(isobutyronitrile) (AIBN) in N, N-dimethylformamide (DMF) was introduced into a pre-treated, silanised, fused-silica capillary by a thermal non-covalent polymerisation procedure. Optimised conditions for the polymerisation reaction were assessed by the separation efficiency of the template. Both the template/monomer/cross linker molar ratio and the compositions of the functional monomer, cross-linker, and porogen affected polymerisation. The optimum in situ polymerisation reaction was performed at 65 °C for 17 min. By varying CEC parameters like eluent composition and pH, we observed that the addition of SDS to the eluent clearly improved the CEC separations. With a mobile phase of citrate buffer (10 mM, pH 3)/SDS (40 mM)/acetonitrile (2/2/1, v/v/v) solution and an applied voltage of 10 kV, the six related structures of the template and their enantiomeric mixtures were satisfactorily separated at 30 °C.