MIL-125-NH₂@Co-HHTP based solid phase microextraction for vulcanization accelerators determination in water samples...

Vulcanization accelerators (VAs) are persistent toxic pollutants threatening aquatic environments and human health, making trace detection challenging. Herein, a MOF-on-MOF heterojunction (MIL-125-NH₂@Co-HHTP) was constructed as a novel solid-phase microextraction (SPME) coating. Coupled with gas chromatography-flame photometric detection (GC-FPD), the method enabled efficient determination of benzothiazole (BTA), 1,3-diphenylguanidine (DPG), and N-cyclohexyl-2-benzothiazolesulfenamide (CBS) in water samples. Under optimized conditions, wide linear ranges (0.5-200 μg L^-1) were obtained for all three analytes, with limits of detection of 0.14-0.29 μg L^-1 and limits of quantification of 0.48-0.95 μg L^-1. Enrichment factors ranged from 22.2 to 60.1. Intra-day and inter-day RSDs (n = 3) were below 6.55% and 8.36%, respectively. The fiber was reusable for >40 cycles, and batch-to-batch RSD (6.35-9.27%) indicated good fabrication reproducibility. Compared with a commercial fiber, the proposed coating showed superior extraction performance for trace VAs in real water samples, with spike recoveries of 87.5-105.1%. The enhanced performance is attributed to synergistic effects of the heterojunction: amino groups from MIL-125-NH₂ facilitate hydrogen bonding, while Co-HHTP provides a planar π-conjugated system for π-π stacking. Interwoven nanorods generate slit-like pores improving active site accessibility. FTIR, XPS, and electrostatic potential calculations revealed that VAs are immobilized via hydrogen bonding, π-π stacking, hydrophobic, and coordination interactions, accompanied by interfacial proton transfer and electron rearrangement. This work provides a sensitive, reliable method for monitoring trace VAs in aquatic environments and highlights the potential of MOF-based heterojunction coatings in sample preparation.