Dispersive micro-solid-phase extraction of aflatoxins from commercial soy milk samples using a green vitamin-based metal-organic framework as an efficient sorbent followed by high performance liquid chromatography-tandem mass spectrometry determination

Abstract

In the current work, for the first time, a vitamin-based metal-organic framework constructed from cobalt ions and vitamin B₃ has been used as a sorbent in dispersive micro-solid-phase extraction. The proposed method was used to extract and enrich aflatoxins (B₁, B₂, G₁, and G₂) from soy milk samples before their quantification by high performance liquid chromatography-tandem mass spectrometry. In this work, first the metal-organic framework was synthesized and characterized using techniques such as X-ray diffraction, Fourier transform infrared spectrophotometry, scanning electron microscopy, nitrogen adsorption/desorption, and energy-dispersive X-ray spectroscopy. Then it was used as an efficient sorbent in the proposed dispersive micro-solid-phase extraction. For this purpose, after precipitating the proteins of soy milk sample with the aid of trichloroacetic acid, the supernatant phase was taken, mixed with the synthesized sorbent, and vortexed. After centrifuging, the analytes loaded on the adsorbent were eluted with methanol to transfer them into an organic phase which was compatible with the subsequently employed separation system. The adsorption capacity of the synthesized MOF for aflatoxins B₁, B₂, G₁, and G₂ were 0.77, 0.83, 0.70, and 0.54 mg g^-1, respectively. Under the best experimental situations, satisfactory outcomes including acceptable extraction recoveries (64-75%), low limits of detection (11.3-48.2 ng L^-1) and quantification (42.8-161.6 ng L^-1), and good repeatability (relative standard deviations equal or less than 4.0 and 4.7% for intra- and inter- day precisions, respectively) were obtained. In addition, green synthesis of the metal-organic framework (using vitamin B₃ as a linker, water as the reaction solvent, and mild conditions) and usage low amount or volume of the adsorbent and organic solvents during the extraction process were the other beneficial aspects of this work which caused the suggested analytical method to be environmentally friendly.

Keywords: Aflatoxin; Dispersive micro–solid–phase extraction; High performance liquid chromatography; Metal–organic framework; Soy milk.