Surface Ionization Strategy of Monodisperse Magnetic Nanospheres Boosting the Extraction Selectivity for Aristolochic Acid I in Traditional Chinese Patent Medicines

Cationic polymer-grafted particles have been identified as promising separation materials for acidic molecules. In this study, N,N-dimethylaminopropyl acrylamide (DMAPAm) was used as a cationic monomer and copolymerized with divinylbenzene (DVB) onto the surface of monodisperse magnetic nanoparticles. The poly (DVB-co-DMAPAm) layer exhibit amphiphilic property similar to that of the poly (DVB-co-NVP) layer prepared in our previous work. During observation of adsorption and desorption properties of this nanocomposite for compounds with different ionization modes, the nanocomposite demonstrated efficient adsorption and desorption for aristolochic acid I (AAI), while low efficiency for the amphoteric and basic compounds. The adsorption selectivity for AAI was attributed to (1) the electrostatic interaction with the cationic moiety of copolymer and (2) the hydrophobic and π-π stacking interactions from the aromatic ring of copolymer. Based on these properties, a simple and fast magnetic solid phase extraction (MSPE) method coupled with HPLC was developed for quantification of AAI in traditional Chinese patent medicines (TCPM). This method was proved to be robust in the analysis of real drug samples, which was characterized by good linearity (R2=0.9999), high recoveries (90.4%-98.9% when spiked at 0.05-1.0 μg mL-1) and a satisfactory repeatability (relative standard deviation below 3.9%, n=6). Additionally, the proposed nanocomposite could be reused for six cycles without a significant loss of extraction capability, highlighting the merits of stability and reusability.