Covalent organic frameworks with tunable pore sizes enhanced solid-phase microextraction direct ionization mass spectrometry for ultrasensitive and rapid analysis of tetrabromobisphenol A derivatives

Selective adsorption via the size matching effect is one of the most effective strategies for separating and analyzing low levels of organic molecules. Herein, multicomponent covalent organic frameworks (MC-COFs) with tunable pore sizes are constructed by using one knot (1,3,5-triformylphloroglucinol, Tp) and two organic linkers (p-phenylenediamine, Pa; benzidine, BD). The pore sizes of the MC-COFs composed of TpPaBDX (X = [BD]/([Pa] + [BD]) × 100 = 0, 25, 50, 75, and 100) range from 0.5–1.5 to 0.5–2.2 nm due to variations in the initial organic linker ratios. When coupling TpPaBDX-based solid-phase microextraction (SPME) with constant flow desorption ionization mass spectrometry (CFDI-MS), these MC-COFs feature better selective adsorption performance for tetrabromobisphenol A (TBBPA) derivatives than TpPa with a smaller pore size, TpBD with a larger pore size and even some commercial fibers (e.g., polydimethylsiloxane/divinylbenzene (PDMS/DVB)-, polyacrylate (PA)- and PDMS-coated fibers). The improved method involving MC-COF TpPaBD50 also presents favorable stability with relative standard deviations (RSD, 1 μg L−1) for single fibers of 5.5–7.9% (n = 7) and fiber-to-fiber of 6.6–7.8% (n = 7). Due to the decreased limits of detection and quantification (0.5–12 and 1.6–40 ng L−1), and reduced separation and detection time (7 min), ultratrace levels of TBBPA derivatives in real water samples are successfully detected. The proposed method shows great potential for the rapid tracing of the distribution, transportation and transformation of TBBPA derivatives to better understand their ecotoxicological effects in environmental media.