Molecularly imprinted polymers based on multi-walled carbon nanotubes for selective solid-phase extraction of oleanolic acid from the roots of kiwi fruit samples

This study describes the synthesis of novel molecularly imprinted polymers based on multi-walled carbon nanotubes (MWNTs@MIPs) using oleanolic acid as the template, 4-vinylpyridine as the functional monomer and divinylbenzene as the cross-linker by heat-induced polymerization. The MWNTs@MIPs were characterized with Fourier transform infrared (FT-IR) spectrometry and scanning electron microscopy (SEM). The adsorption process of the MWNTs@MIPs towards oleanolic acid was investigated in detail. The properties of MWNTs@MIPs for solid-phase extraction (SPE) were also evaluated. The results demonstrated the good imprinting effect and the comparable selectivity of MWNTs@MIPs. The optimized molecularly imprinted solid-phase extraction (MISPE) procedure was applied to extract oleanolic acid from the extracts of the roots of kiwi fruit samples. The recoveries of spiked oleanolic acid in kiwi fruit samples were in the range of 84–92.6% with relative standard deviations below 5%, and its limit of detection reached 2.56 μg L−1.