Fluorine-Functionalized Covalent Organic Framework as Efficient Solid Phase Extraction Sorbent for Adsorption of Aflatoxins in Nuts

Abstract

Aflatoxins as naturally occurring carcinogenic biotoxins pose a significant public health risk. In this study, a novel fluorine-functionalized covalent organic framework (F-COF) and a non-fluorine-functionalized COF (H-COF) were fabricated by the direct polycondensation of tris(4-aminophenyl)amine and 2,3,5,6-tetra-fluoroterephthaldehyde or terephthalaldehyde under solvothermal conditions. Compared with the H-COF, the F-COF provided more active sites for aflatoxins adsorption, resulting to a remarkably enhanced adsorption capability to aflatoxins. The favorable adsorption of aflatoxins was attributed to multiple interactions including pseudo hydrogen bond, F-O, F-π, π-π interactions and hydrophobic interactions between F-COF and aflatoxins. By coupling F-COF based solid phase extraction technique with high-performance liquid chromatography instrument equipped with a fluorescence detector, a rapid and sensitive method for determining aflatoxins in nuts (peanuts and pistachios) was established. Under optimal conditions, the limits of detection for aflatoxins were 0.02-0.30 ng g-1. The linear range was 0.08-16.0 ng g-1 and the recoveries of the F-COF-based method were 83.5%-114% with relative standard deviations less than 8.0%. This work not only provides a viable analytical strategy for aflatoxins but also offers a new idea to prepare effective sorbents with specific functional groups for the adsorption and enrichment of specific targets.

Keywords: Aflatoxins, Solid phase extraction, Fluorine-functionalized covalent organic frameworks, Nuts, Determination.