Simultaneous determination of bifenox, dichlobenil and diclofop methyl by hollow carbon nanospheres enhanced magnetic carboxylic multi-walled carbon nanotubes.

A novel analytical method based on magnetic solid-phase extraction (MSPE) coupled with high performance liquid chromatography-diode array detection (HPLC-DAD) was established for three herbicides simultaneous determination. The key of the method was the explored extractant, which was a composite of hollow carbon nanospheres (HCSs) enhanced magnetic carboxylic MWCNTs (HCSs@Fe3O4-MWCNTs-COOH). MWCNTs-COOH was inserted in the pores of HCSs by oscillation and sonication with the capillary forces, making the carboxylic groups and structure intervals of the composite increase as compared to MWCNTs-COOH, therefore the extractant exhibited enhanced hydrophilicity, dispersibility, adsorptivity and selectivity. The extractant was sensitive to analytes with the structure of multi-aromatic ring, more hydrogen bond acceptor and large molecular polar surface area, which can be attributed to hydrogen bonding and π-π electron-donor-acceptor (EDA) interactions. The morphology, structure and magnetic property of the extractant were characterized. Then the explored extractant based MSPE-HPLC-DAD method was applied for bifenox (BFO), dichlobenil (DCB) and diclofop methyl (DCM) determination from wheat flour samples. Prior to real sample analysis, critical extraction parameters such as solution pH, extraction time, salt addition and temperature were investigated and optimized, and the analytical method was evaluated. It was indicated that the method had satisfactory linearities with the linear coefficients above 0.99, good precision with the RSD less than 3.5%, desirable recoveries ranged from 88.8% to 96.6%, and low limits of detection (LOD) that were 0.39, 0.24, and 0.68 ng/g for DCB, BFO and DCM, respectively. The established MSPE-HPLC-DAD method has great potentials for trace polar herbicides selective determination from complex matrix samples.