Waste toner powder contains carbon and ferrosoferric oxide, meaning it has potential as a magnetic adsorbent. Previous efforts have tried to improve its hydrophilicity for aqueous samples, but not non-aqueous food matrices such as edible oils. In this work, we proposed a one-step hydrothermal carbonization method using 50 % (v/v) acetic acid to prepare carboxyl-functionalised magnetic adsorbent for aqueous and oil-based food samples. Owing to the complexation of carboxyl groups and electrostatic attraction, the adsorption capacity for Pb(II) was 50.3 ± 0.4 mg g−1. Combined with GFAAS, the developed method demonstrated a high enhancement factor (91.0), a low detection limit (0.013 μg L−1) and was also validated by the certified standard reference material, including environmental water, rice flour and tea. Furthermore, successful applications were demonstrated in tap and lake water, orange juice, edible oil and mushrooms with recoveries ranging from 84.4 to 108 %.
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