Selective extraction and determination of catecholamines in urine samples by using a dopamine magnetic molecularly imprinted polymer and capillary electrophoresis

A rapid and selective method for the extraction and determination of catecholamines (CLs) from urine samples has been successfully developed using a magnetic molecularly imprinted polymer (MMIP) as a sorbent material. The MMIP has been prepared using dopamine hydrochloride (DA) as template molecule, methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EDMA) as cross-linking agent and Fe3O4 magnetite as magnetic component. The extraction was carried out by stirring urine samples with the magnetic polymer. When the extraction was completed, the MMIP, together with the captured analytes, was easily separated from the sample matrix by an adscititious magnet. The analytes desorbed from the MMIP were determined by capillary electrophoresis (CE). It was shown that the MMIP had high affinity and selectivity toward DA and other structurally related CLs such as 3-methoxytyramine hydrochloride (MT), DL-normetanephrine hydrochloride (NME), DL-norephinephrine hydrochloride (NE) and (±) epinephrine (E). Different parameters affecting the extraction efficiency were evaluated in order to achieve the optimal pre-concentration of the analytes and to reduce non-specific interactions. Under the optimal conditions, the CL limits of detection were at the 0.04–0.06 μM range. The relative standard deviations of migration time and response ranged from 0.7% to 1.4% and from 2.9% to 5.5%, respectively. The proposed method was successfully applied to determine CLs, including MT, NME, DA, NE and E in human urine samples.