Ultrasound-assisted rapid growth of chemically bonded bifunctional mesoporous covalent organic framework submicrospheres on a nickel-chromium alloy support for efficient solid-phase microextraction of bisphenols from water and milk samples.

A layer-by-layer chemical bonding strategy was developed for fast in situ growth of bifunctional mesoporous covalent organic framework submicrospheres (COF SMSs) on the nickel-chromium alloy (Ni-Cr) fiber substrate via the ultrasound-assisted Schiff-base reaction for the first time. COF SMSs showed well-defined morphology, extraordinary high surface area (1211 m·g) and narrow mesopore (2.50 nm) as well as excellent stability. Furthermore, the resulting Ni-Cr fiber presented outstanding adsorption capability and improved selectivity for bisphenols (BPs). Consequently, an attractive SPME-HPLC-UV approach with the Ni-Cr@Ni-Cr LDHs NSs@COF SMSs fiber was proposed for rapid preconcentration and sensitive determination of BPs. By optimizing adsorption parameters, the SPME-HPLC-UV method presented good linearity for five BPs in the ranges of 0.02-200 ng·mL with coefficients of determination (R) higher than 0.999. Limits of detection and limits of quantitation were obtained from 0.003 ng·mL to 0.006 ng·mL and from 0.010 to 0.019 ng·mL, respectively. Moreover, the intra-day and inter-day precision expressed as relative standard deviations (RSDs) was 1.57-3.52 % and 2.65-4.38 % for the proposed method with a single fiber, respectively. RSDs of the proposed method with different duplicate fibers were 3.25-6.72 %. The proposed SPME-HPLC-UV method was available for efficient preconcentration and sensitive detection of five BPs from real water and milk samples. The relative recoveries at three spiking levels of BPs were achieved in the range of 80.00-118.8 % with RSDs below 7.81 %. In addition, the prepared fiber still exhibited satisfactory adsorption performance after 120 adsorption-desorption cycles.