Carbonized metal-organic framework-74/carbon aerogel composites for the efficient extraction of triazole fungicides from fruits and vegetables

To improve the extraction efficiency, availability, and stability of metal-organic framework (MOF) for pipette-tip solid-phase extraction (PT-SPE), a carbonized MOF-74/carbon aerogel composite (CMOF-74/CA) was developed. A carbon aerogel with a surface area of 547.7 m2 g-1 was prepared by carbonizing a watermelon peel. After that, via a hydrothermal reaction, the MOF-74 was in situ grown on the surface. After the pyrolysis at 700 °C for 2 h, the CMOF-74/CA composite was obtained. Through regulating the concentration of reactants, a series of MOF-74/CA and CMOF-74/CA materials were prepared. These materials were used to extract hexaconazole and diniconazole in fruits and vegetables before gas chromatography-flame ionization detection (GC-FID). The adsorbent type and amount, sample pH, and the desorption solvent type and volume were optimized factor by factor. Under the optimized conditions, a PT-SPE-GC-FID method was established. Moreover, good linearity in the concentration ranges of 0.098-200.0 mg kg-1 and 0.196-200.0 mg kg-1, and detection limits ranging between 0.033 and 0.065 mg kg-1 were achieved for two triazole fungicides (TFs). The relative standard deviations (n = 3) for intra-day and inter-day tests were in the ranges of 3.1-3.2% and 3.0-3.4%, respectively. The method showed satisfactory analytical performance in different samples with good relative recoveries in the range of 72.6-116%. Compared with some methods, it displayed wider linearity, better or comparable sensitivity, and enhanced analytical precision.