A hydrogel composite prepared from alginate, an amino-functionalized metal-organic framework of type MIL-101(Cr), and magnetite nanoparticles for magnetic solid-phase extraction and UHPLC-MS/MS analysis of polar chlorophenoxy acid herbicides.

A regenerable hydrogel composite is described that is comprised of alginate, amino-functionalized metal-organic framework (MIL-101(Cr)-NH2) and magnetite nanoparticles. The composite was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, vibrating-sample magnetometry and Brunauer-Emmett-Teller measurement. The material was applied to the magnetic solid-phase extraction of six polar chlorophenoxy acid (CPA) herbicides. Specifically, the herbicides clofibric acid, 4-chlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, 2-(2,4-dichlorophenoxy)propionic acid, 2,4,5-trichlorophenoxyacetic acid and 2-(2,4,5-trichlorophenoxy)propionic acid were extracted from environmental aqueous samples and analyzed by ultra-HPLC-tandem mass spectrometry. The abundance of hydroxyl and carboxyl groups on the natural polymer renders alginate a superior hydrophilic coating. It brings the polar acidic herbicides into closer proximity to the porous metal-organic framework. When integrated with MIL-101(Cr)-NH2, the composite material combines the favorable attributes of high hydrophilicity and large adsorption capacity. An orthogonal array design matrix was employed for the optimization of the extraction parameters. Under the most favorable conditions, the method displays a wide linear response and low limits of detection (0.43-16 ng⋅L-1). Precision and reproducibility (with relative standard deviations of ≤13%) are satisfactory. Enrichment factors range between 27 and 107. The composite was applied to the extraction of CPA herbicides from lake and pond water samples. A markedly improved sorbent-based extraction procedure and performance (compared to previous methods) is found. Graphical abstract Schematic of the magnetic solid-phase extraction of polar herbicides using a hydrogel composite as sorbent. The amino-functionalized MIL-101(Cr) and hydrophilic alginate work in synergy resulting in a material which possess favorable attributes of both components that are beneficial for extraction.