Nano-sized FeO@SiO-molecular imprinted polymer as a sorbent for dispersive solid-phase microextraction of melatonin in the methanolic extract of Portulaca oleracea, biological, and water samples.

In this study, a magnetic molecularly imprinted polymer (MMIP (FeO@SiO-MIP)) was used for the dispersive magnetic solid-phase microextraction (d-MSP-μ-E) to design an easy and effective method for melatonin (MLT) extraction in the methanolic extract of Portulaca oleracea, human urine and plasma, and water samples. HPLC with UV detection was utilized, and pH, the type and volume of eluent, MMIP mass, and contact time were considered as effective factors in the study of MLT separation and pre-concentration. These factors were optimized by Plackett-Burman and multi-objective response surface methodology (RSM). The values were 10 mg, 14 min, 4.2, methanol, 0.180 mL, 2.5 min, for the MMIP mass, time of sorption, sample pH, eluent type, eluent volume, and time of elution, respectively. At the optimum conditions, the limit of detection (LOD) was 0.046 ng mL, and the limit of quantification (LOQ) was 0.156 ng mL. The sorption capacity of the proposed MMIP sorbent was 109.1 mg g at the optimum conditions. Besides, linear dynamic range (LDR) was 0.2-4200 ng mL, and the precision of the method (RSD %) for triplicate measurements was <6.1%. The MMIP showed saturation magnetization of 19.75 emu g, resulting in fast separation of the sorbent. The sorption test revealed the high sorption capacity of the MMIP for MLT and its homogeneous binding sites. In all spiked levels (50, 100, 200, and 500 ng mL), 93.07-104.1% was the range obtained for the recovery of MLT. The relative selectivity factor (β) values of MLT/tryptophan, MLT/serotonin, MLT/ferulic acid, MLT/mefenamic acid, MLT/quercetin, MLT/luteolin, and MLT/chlorogenic acid were 1.60, 1.68, 2.02, 2.38, 2.32, 2.40, and 2.50, respectively. The results of desorption-regeneration cycles (seven times) by employing the MMIP showed the high stability of the resultant material. In conclusion, the MMIP combined with the magnetic separation showed a specific sorption behavior for MLT and suggested a simple, flexible, selective, and powerful analytical tool.