Solvent-loaded metal-organic framework of type MIL-101(Cr)-NH2 for the dispersive solid-phase extraction and UHPLC-MS/MS analysis of herbicides from paddy field waters.

A novel solvent-loaded dispersive solid-phase extraction (SL-DSPE) method integrated with liquid-phase microextraction (LPME) has been developed by the direct loading of solvent into the pores of a metal-organic framework (MOF), MIL-101(Cr)-NH2. Despite numerous advantages of MOFs, they are usually highly hydrophobic which limits their dispersibility and therefore effective contact with the analytes in aqueous samples. To overcome this and promote its interactions with polar compounds, MIL-101(Cr) was functionalized with -NH2 and loaded with a comparatively polar organic solvent, dichloromethane. The purpose of dichloromethane was to condition the MIL-101(Cr)-NH2, promote LPME of the analytes and facilitate the re-collection of the materials after the extraction. Five chlorophenoxy acid herbicides, including 2,4-dichlorophenoxyacetic acid, 2,4,5-trichlorophenoxyacetic acid, 4-chlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, and 2-(2,4,5-trichlorophenoxy)propionic acid, were studied and determined by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). MIL-101(Cr)-NH2 was characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, and surface area measurement. Several extraction parameters were optimized, and under the most favorable conditions, the SL-DSPE-UHPLC-MS/MS method achieved enrichment factors between 25 and 66. Low limits of detection (2.66-19.7 ng·L-1) and wide dynamic working ranges with good linearity (r2 ≥ 0.991) were attained for all analytes. The method was repeatable, with intra- and inter-day relative standard deviations (RSDs) below 4.5 and 7.6%, respectively, for three replicate determinations. The application of SL-DSPE-UHPLC-MS/MS to paddy field waters gave satisfactory relative recoveries ranging between 80.2 and 108%, with RSDs better 8.4%. Several of the CPAs were detected in these samples. Graphical abstract Schematic of the solvent-loaded dispersive solid-phase extraction procedure. By directly loading dichloromethane into the pores of MIL-101(Cr)-NH2, this method improves the extraction capability of the sorbent through the combination of solvent- and sorbent-based microextraction.