Analysis of mycotoxins in grain samples using 3D covalent organic frameworks and stable isotope labeling technique

A new three-dimensional (3D) covalent organic framework (COF) tris (4-formylphenyl) amine-tetra (4-aminophenyl) methane (TFPA-TAM) was designed and synthesized. It was used in the dispersed solid-phase extraction (DSPE) of mycotoxins from grain sample extractant. The adsorption performance of 3D COF (TFPA-TAM) was compared with four kinds of different COFs with various spatial structures and steric hindrances to illustrate the key factors in the adsorption process. Stable isotope labeling (SIL) strategy with dansyl chloride (DNS-Cl) and deuterated dansyl chloride (d6-DNS-Cl) as labeling agents was applied for the first time in the high-performance liquid chromatography-tandem mass spectrometry (HPLC–MS/MS) quantitation of mycotoxins. SIL strategy enhanced the mass spectrometry (MS) sensitivity and minimized matrix effects. The optimized adsorption conditions were sample solution pH 7; adsorbent amount, 20 mg; desorption time, 5 min; elution volume, 1 mL. The limits of detection (LODs) of mycotoxins in grain samples were in the range of 4–7 µg/kg, while limits of quantification (LOQs) were in the range of 13–24 µg/kg. The linearity coefficients for all analytes were higher than 0.9977. The recoveries of this method were in the range of 90.3–94.3% with relative standard deviations of <6.3%, and the matrix effects were in the range of 93.5–98.8%.