Synthesis of molecular imprinted polymer nanoparticles followed by application of response surface methodology for optimization of metribuzin extraction from urine samples

A molecular imprinted polymer was prepared with precipitation polymerization technique and applied as a sorbent for selective extraction and enrichment of metribuzin herbicide prior to high performance liquid chromatography. Optimization of critical variables affecting the efficiency of molecularly imprinted solid-phase extraction (MISPE), such as sorbent mass, sample pH and flow rate of sample, volume, concentration, and flow rate of elution solvent was done by employing central composite design (CCD) of the response surface methodology. Two separate models were developed for the adsorption and recycling steps. The analysis of variance (ANOVA) demonstrated that, experimental data were excellently fitted to the proposed response models. The optimum operating conditions were: a sorbent mass of 25mg, sample pH 6.19, sample flow rate of 2.15mL/min, and a 5mL portion of methanol/acetic acid with 92.7:7.3 (v/v) ratio and flow rate of 2.1mL/min for the extraction process. Under the optimized conditions, the linear range was obtained from 20 to 120 mu g/L (R-2=0.999) and the lowest detectable concentration (LOD) and the lowest quantitative concentration (LOQ) were calculated as 5.75 and 19.86 mu g/L, respectively. Finally, the designed MISPE method was successfully applied to determine trace amount of metribuzin in real samples. The diluted urine samples were spiked with metribuzin at 4 levels and extracted with recoveries ranging from 93.82 to 97.84% and the relative standard deviation (RSD) less than 4.8%.