Fluorine-functionalized covalent organic framework as efficient solid phase extraction sorbent for adsorption of aflatoxins in nuts.

In this study, a new fluorine-functionalized covalent organic framework (F-COF) was designed and fabricated by the direct polycondensation of tris(4-aminophenyl)amine and 2,3,5,6-tetra-fluoroterephthaldehyde for the first time. F-COF exhibited a remarkably enhanced adsorption capability compared with that of the fluorine-free COF. The favorable adsorption of aflatoxins was attributed to multiple interactions including pseudo hydrogen bond, F-O, π-π, F-π interactions and hydrophobic interactions between F-COF and aflatoxins. By coupling F-COF based solid phase extraction with high-performance liquid chromatography equipped with fluorescence detector, a rapid and sensitive method for determining aflatoxins (aflatoxin B, B, G and G) in nuts (peanuts and pistachios) was established. Under optimal conditions (35 mg F-COF, 100 mL sample solution, 3 mL min as sample loading rate, pH<7, 0.2 mL acetonitrile as desorption solvent), the limits of detection for aflatoxins were 0.02-0.30 ng g. The linear range was 0.08-16.0 ng g and the recoveries of the F-COF-based method were 83.5-114 % with relative standard deviations less than 8.0 %.