Preparation of hybrid-monomer, double-template molecularly imprinted polymers for the purification of green tea extracts†
Hybrid-monomer double-template molecularly imprinted polymers (HDMIPs) were prepared by two different approaches based on in situ polymerization. The hybrid-monomers were prepared from 3-aminopropyltriethoxysilane (APTES) (the inorganic precursor) and methacrylic acid (MAA)/acrylamide (AM) (the organic precursor). HDMIPs were used as sorbents for the selective isolation of theophylline and quercetin from green tea extracts. Fourier transform infrared and field emission scanning electron microscopy were used to characterize the morphology and structure of the HDMIPs. The recognition ability and binding capability of the HDMIPs for selected analytes were evaluated by static absorption and Scatchard analysis. The adsorption equilibria of the two analytes were investigated using three different analysis models: linear, Langmuir and Freundlich. With optimization of the solid-phase extraction procedure, a reliable analytical method was developed for recognition of theophylline and quercetin in green tea, with outstanding extraction recoveries of 96.68% and 88.92%, respectively. Using the proposed method, the recoveries at three spiked levels of analysis were in the range 84.62–96.68% for theophylline and 82.88–88.92% for quercetin. The HDMIPs therefore demonstrated a high affinity for the two target analytes, suggesting that the proposed approach could potentially offer a novel purification method for complex samples.