Simple and selective detection of quercetin in extracts of plants and food samples by dispersive-micro-solid phase extraction based on core-shell magnetic molecularly imprinted polymers

The objective of this study was to develop a simple, sensitive and selective procedure for the preconcentration and determination of quercetin residues in Apium graveolens, Brassica oleracea, Spinacia oleracea, watercress, onion, and apple matrices. This novel method was developed on the basis of the dispersive-micro-solid phase extraction (D-mu-SPE) procedure based on a core-shell magnetic molecularly imprinted polymer (MMIP) in combination with high-performance liquid chromatography-ultraviolet (HPLC-UV). Variables affecting the quercetin extraction efficiency included pH, MIP dose, extraction contact time, elution organic solvent, and volume of organic solvent and were evaluated by the experimental central composite design (CCD). The obtained optimal parameters were as follows: pH (3.5), sorbent (12 mg), elution organic solvent and solvent volume (methanol, 0.2 mL), and elution time (22.0 min, without adding salt). The calibration curve was linear in the concentration range of 0.6-5500 mu g L-1 with the lower limits of detection found in the range of 0.113-0.117 mu g L-1, thereby revealing the high-sensitivity and -selectivity properties. The combination of D-mu-SPE and HPLC-UV could provide a method for the recovery of the analyte in various matrices at 22 min contact time with good reusability and excellent recoveries at four concentration levels (50, 100, 500, and 1000 mu g L-1), ranging between 95.44 and 106.89% (relative standard deviation <6.0%). Based on competitive sorption experiments, the synthesized MMIP displays higher selectivity toward quercetin compared to non-imprinted polymers (NIPs) and other sorbents.