Facile synthesis of Fe₃O₄@polyethyleneimine modified with 4-formylphenylboronic acid for the highly selective extraction of major catecholamines from human urine.

The levels of catecholamines, especially dopamine, epinephrine and norepinephrine in urine and plasma have been used to assist the diagnosis and treatment of psychosis. Due to their low endogenous concentrations, the determination of the three major catecholamines is very difficult. Boronate adsorbents are often employed to extract these cis-diol compounds from complex matrices. In this work, a novel type of magnetic nanoparticles modified with 4-formylphenylboronic named Fe3O4@PEI-FPBA was synthesized by a facile two-step approach. The abundant amino groups of polyethyleneimine provided the rich binding sites for boronate ligands. Herein, the adsorption capacity of Fe3O4@PEI-FPBA is greatly improved with a value of 3.45 mg/g towards epinephrine, which is much larger than that of analogous material without polyethyleneimine. The magnetic nanoparticles also exhibited high magnetization (72.25 emu/g) and specific selectivity towards the catecholamines. Finally, a liquid chromatography tandem mass spectrometry method based on Fe3O4@PEI-FPBA nanoparticles was successfully used to determine the three catecholamines from human urine samples. The linearity, limit of quantitation, recovery and precision of the method were satisfactory. Based on the method, it is found that the levels of dopamine, epinephrine and norepinephrine in depressive patients are higher than those in healthy controls.