A hybrid material prepared by controlled growth of a covalent organic framework on amino-modified MIL-68 for pipette tip solid-phase extraction of sulfonamides prior to their determination by HPLC.

A hybrid material was synthesized by growing a covalent organic framework (COF) in-situ on the surface of functionalized metal organic framework (MOF). Specifically, the amino-modified MOF (type MIL-68) was obtained by reacting indium(III) nitrate and 2-aminoterephthalic acid. Subsequently, it was reacted with tris(4-formylphenyl)amine and tris(4-aminophenyl)amine to obtain the final hybrid COF. This material overcomes the disadvantage of MOF concerning poor stability in aqueous solution and it combines the advantages of MOF and COF. This MOF@COF hybrid material is shown to be a viable adsorbent for the extraction of sulfonamides by pipette tip solid-phase extraction). Following elution with acetonitrile, the sulfonamides were quantified by high performance liquid chromatography using variable wavelength detection (HPLC-VWD). The structure and morphology of the material was characterized by various techniques. Extraction parameters such as amount of adsorbent, sampling rate, sample pH, elution solvent and sample volume were investigated. Under the optimum conditions, the sulfonamides tested (sulfadimethoxine sulfamethoxazole, sulfamonomethoxine, sulfamethazine, sulfamerazine and sulfadiazine) can be determined over a wide linear range (10-2000 ng·mL-1), with low limits of detection (1 ng·mL-1) and high precision (RSD <5.2%). The method was applied the determination of sulfonamide residues in (spiked) environmental water, milk and meat samples and gave recoveries in the range from 68.9-103.8%, with RSDs of <6.6%. The packed pipette tip column exhibits excellent stability, reproducibility and high adsorption capacity. Graphical abstract A hybrid sorbent was prepared by controlled growth of a covalent organic framework on amino-modified MIL-68 and packed into a pipette tip for sulfonamide extraction. The sensitivity was dramatically increased after optimized extraction, with limit of detection as low as 1 ng·mL-1.