Preparation Of Methacrylate Monolithic Column And Its Application As Solid Phase Extractor For Benzoylurea Insecticides Residues In Fruit

Objectives The direct detection of benzoylurea insecticides(BUs) residues in fruits is difficult, because of complexity of the fruit sample and the extremely low concentrations of the analytes. Therefore, solid-phase extraction(SPE) is an effective sample preparation method for removal of interfering compounds and enrichment of analytes. Here, a hydrophobic 2-ethylhexyl methacrylate based monolithic column was fabricated and developed as a reusable sorbent, coupled with high performance liquid chromatography for determination of diflubenzuron and hexaflumuron in fruits.Methods 1 The hydrophobic monolithic column was prepared in a stainless steel column(10 mm × 4.6 mm i.d.) via in-situ copolymerization of 2-ethylhexyl methacrylate(EHMA) monomer and ethylene dimethacrylate(EDMA) as crosslinking agent. Then, the ratios of monomer and crosslinking agent, porogens variety and ratios of porogens were investigated. The prepared columns were aslo characterized by scanning electron microscope and nitrogen adsorption-desorption. 2 The optimization extraction parameters including loading solvent, flow rate of loading, eluting solvent and flow rate of eluting were conducted. The loading solvent were optimized by pure water, 0.1% and 0.5% formic acid, 5 and 10 mmol/L ammonium acetate solution. Acetonitrile, methanol, 0.1% and 0.5% formic acid in acetonitrile were evaluated as eluting solvent. The flow rate of loading(0.1-0.5 m L/min) and eluting(0.3-1.0 m L/min) were investigated. 3 The linearity range, the limit of detection(LOD), the limit of quantification(LOQ), recovery and precision of the proposed method were investigated under the optimum experimental conditions. And the reusability and reproducibility of the poly(EHMA-co-EDMA) monolithic extractors were also assessed by calculating the relative standard deviations(RSDs) of the extracted peak area of diflubenzuron and hexaflumuron in fruits.Results 1 The monolithic column was prepared with the mixyure of dodecanol and N, N-dimethyl formamide(DMF)(5:1, V/V), EHMA and EDMA(1:5, mole ratio). The scanning electron microscope image demonstrated the distinct continuous porous structure of the monolith. The surface area was found to be 164.01m2/g. 2 The determination of diflubenzuron and hexaflumuron in fruits was achieved using poly(EHMA-co-EDMA) monolithic column as SPE sorbent combined with high performance liquid chromatography(HPLC). The SPE was achieved using 5 mmol/L ammonium acetate solution as the loading solvent at the flow rate of 0.1 m L/min. The analytes was eluted by acetonitrile at the flow rate of 1.0 m L/min, and then the analytes was separated by a C18 column. 3 For the proposed method, an excellent linearity for diflubenzuron and hexaflumuron were achieved over the concentration range of 0.1-50.0 mg/m L with a correlation coefficient(r) value above 0.998. The limits of detection(LOD) were 0.0072, 0.009 mg/kg and the limits of quantitation(LOQ) were 0.024, 0.03 mg/kg for diflubenzuron and hexaflumuron. Recoveries obtained for the determination of diflubenzuron and hexaflumuron in spiking samples ranged from 89.5% to 102%, with the relative standard deviations(RSD) below 6.83%. Satisfactory repeatability was achieved, with the RSD of peak area for the 1st, the 25 th and the 75 th injection of diflubenzuron and hexaflumuron were both less than 5.2%.Conclusions Poly(EHMA-co-EDMA) monolithic column developed as a reusable SPE sorbent coupled with HPLC for the determination of diflubenzuron and hexaflumuron residues in fruits. It had been demonstrated that the proposed method can be used for routine determination of diflubenzuron and hexaflumuron in fruits. Compared with the traditional disposable solid phase extraction sorbents, the monolithic sorbent had the advantages of easy preparation and satisfactory reusability.