Reduced graphene oxide-zinc iron oxide nanomaterial as selective dispersive solid-phase extraction sorbent for extraction and enrichment of aflatoxins from milk combined with UHPLC-MS/MS analysis

Fungal species capable of producing aflatoxins frequently contaminate the feed provided to dairy animals, leading to the subsequent occurrence of aflatoxin contamination in milk. Milk is renowned for its exceptional nutritional composition, and the consumption of milk contaminated with aflatoxins by humans can engender a multitude of health complications. In this study, reduced graphene oxide zinc iron oxide (rGO-Zn/Fe2O4) nanomaterial was utilized as a dispersive solid phase extraction adsorbent to separate and enrich aflatoxins (aflatoxin B1, aflatoxin B2, aflatoxin G1, aflatoxin G2, and aflatoxin M1) from milk. The rGO-Zn/Fe2O4 nanomaterial was morphologically characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction, indicating that Zn/Fe2O4 nanoparticles were embedded on the surface of rGO. The acetonitrile/formic acid (99/1, v/v) combined with ultrasonic treatment for a duration of 40 min expressed an efficient extraction solvent. Employing the matrix-spiked technique, different parameters of the dispersive solid-phase extraction (d-SPE) method were meticulously optimized, yielding the following conditions: 2% acetonitrile as loading solvent, 15 mg of rGO-Zn/Fe2O4 as the adsorbent quantity, 15 min of ultrasonication as adsorption time, and n-hexane as the washing solvent. The desorption reagent was 5 mL acetonitrile, with a desorption time of 5 min. The combination of the dispersive solid-phase extraction (d-SPE) technique with validated UHPLC-MS/MS quantitative analysis demonstrated excellent selectivity, a robust linear relationship (R2 ≥ 0.994), remarkable sensitivity (limit of quantification ranging from 0.006 to 0.013 µg/L), and satisfactory recovery rates of 78%–104% at three different matrix-spiked levels. Moreover, the method exhibited precision with relative standard deviations (RSD) ranging from 2.4% to 10.8%. Following appropriate pretreatment procedures, the milk samples underwent rigorous aflatoxin analysis, leading to the identification of AFM1 presence in all of the examined milk samples (n = 9). However, the contamination levels detected were found to be within the permissible limits as defined by regulatory standards.