Hydroxyl-functionalized hollow microporous organic network fiber membranes: fabrication and application in solid-phase extraction of endogenous salicylic acid from plants.

Membrane-based adsorbents serve as core functional materials for the rapid analysis of trace substances. However, the inherent trade-off between permeability and adsorption capacity generally limits the analytical performance of membrane-based micro-solid phase extraction (M-μSPE) in trace detection. To address this limitation, a hydroxyl-functionalized microporous organic network (MON-OH) membrane was fabricated in this study. Its unique hollow porous structure and abundant hydroxyl active sites effectively balanced the permeability and adsorption performance during extraction. A highly sensitive method for the detection of endogenous salicylic acid (SA) in plants was established by coupling MON-OH-based M-μSPE with HPLC-MS/MS. The results showed that the method had excellent analytical performance, with a wide linear range (1.5-1000.0 pg mL-1), a good Pearson correlation coefficient (R ≥ 0.9993), a low limit of detection (0.5 pg mL-1), and good reproducibility (RSD ≤ 5.6%, n = 6). This method successfully detected trace levels of salicylic acid (SA) ranging from 1.5 to 50.1 ng g-1 in tomato roots, stems and leaves. The data revealed that SA in different plant tissues exhibited divergent response patterns under Cd stress, and an obvious concentration threshold existed for SA to respond to Cd exposure. This work demonstrates the outstanding application potential of MON membranes in sample pretreatment and offers a novel synthetic strategy for functionalized MON membranes.