Rapid Construction of Covalent Organic Framework Submicrospheres on A Nickel-Chromium Alloy Support for Efficient Solid-phase Microextraction of Bisphenols from Water and Milk Samples

To address the critical challenge of achieving robust immobilization of high-performance coatings in solid-phase microextraction (SPME), a novel ultrasound-assisted rapid bonding method was developed in this work. A nickel-chromium (NiCr) alloy wire with excellent mechanical properties was utilized as the supporting substrate, onto which functionalized layered double hydroxide (LDH) nanosheets were employed as an intermediate bridge layer for the first time. This strategy facilitated the rapid covalent grafting of covalent organic framework submicrospheres (COF SMSs) onto the fiber surface, thereby yielding a uniform LDH@COF SMSs composite coating with strong interfacial adhesion. Compared with commercial polydimethylsiloxane (PDMS) and PDMS/divinylbenzene (DVB) fibers, the fabricated NiCr@NiCr LDHs@COF SMSs fiber demonstrated excellent adsorption performance and good extraction selectivity for bisphenols (BPs). Thus, a SPME-high performance liquid chromatography-ultraviolet dection (HPLC-UV) method was proposed for rapid pre-concentration and highly sensitive detection of BPs. Under the optimal experimental conditions, the established method showed excellent linearity in the BPs concentration range of 0.02‒200 μg/L, with a determination coefficient ( R2 )>0.9990. The limits of detection (LODs) and limits of quantification (LOQs) were 0.003‒0.006 μg/L and 0.010‒0.019 μg/L, respectively. Relative standard deviations (RSDs) for intra-day and inter-day analyses ranged from 1.46% to 3.41% and from 2.70% to 4.49%, respectively. The developed method with the constructed fiber was applied to preconcentration and detection of different types of BPs in real samples, showing satisfactory recoveries ranging from 80.0% to 118.8%. Besides, the NiCr@NiCr LDHs@COF SMSs fiber could maintain good extraction performance even after 120 extraction-desorption cycles.