Determination of Aflatoxins in Tea by Magnetic Solid Phase Extraction Based on Covalent Organic Framework Coupled with High Performance Liquid Chromatography-Tandem Mass Spectrometry

A magnetic solid phase extraction (M-SPE) based on covalent organic framework materials coupled with high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the efficient determination of four aflatoxins (AFs) in tea. The samples were extracted with a mixture of acetonitrile, water and glacial acetic acid (8.0:1.9:0.1, V/V) and centrifuged. The supernatant was evaporated to almost dryness, re-dissolved in water and pH adjusted, extracted M-SPE and filtered, and the filtrate was detected in the positive ion mode. The calibration curves for all analytes were linear in the range of 0.05–50 μg/L with coefficients of determination (R²) > 0.999 2, the spiked recoveries were in the range of 67.6%-103.7%, and the relative standard deviations (RSDs) for intra- and inter-day precisions were less than 9.24%, the limits of detection (LODs) were in the range of 0.01-0.06 μg/kg, and the limits of quantification (LOQs) of the developed method were in the range of 0.05-0.20 μg/kg. The covalent organic framework material prepared in this study has a strong adsorption capacity for AFs, and M-SPE-HPLC-MS/MS is suitable for the rapid, highly sensitive and accurate detection of AFs in tea.