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A magnetic dispersive micro-solid phase extraction procedure for the determination of the thallium content in waters is presented. The incorporation in the sample (10 mL) of a small amount of graphene-Fe3O4 composite (3.6 mg) in the presence of 10-4 mol L-1 Aliquat 336 at pH 2 results in the complete retention of both thallium(I) and thallium(III). After separation with a magnet, the micro-solid phase recovered is treated with 0.05 mL of a 0.1 mol L-1 sodium ethylenediaminetetracetate solution at pH 9, and the supernatant obtained afte