Graphene/multi-walled carbon nanotubes as an adsorbent for pipette-tip solid-phase extraction for the determination of 17β-estradiol in milk products.

The illegal addition and abuse of 17β-estradiol (E2) in food has led to its accumulation in the body through the food chain, resulting in adverse effects on the human body through interference with the endocrine system. Because milk and dairy products are major components of the human diet, screening as well as quantitative analysis of E2 in these food types is important. In this work, a three-dimensional graphene/multi-walled carbon nanotube composite was synthesized and applied to a home-made pipette-tip solid-phase extraction cartridge and coupled with high-performance liquid chromatography-fluorescence detection to determine E2 in milk. The established method showed good linearity in the range of 5-250 ng mL with correlation coefficient of 0.9998. The detection limit and quantitation limit were 0.7 and 2.3 ng mL, respectively. The repeatability and intermediate precision, expressed as the coefficient of variation were 3.7% and 6.0%, respectively. The accuracy of the method was investigated by recovery experiments with milk at three spiked levels (25, 100, and 250 ng mL), where the recoveries were in the 88.4-108.9% range with relative standard deviations ≤5.5%. The proposed method has the advantage of requiring less adsorbent (only 1.0 mg) and less organic reagent (1.0 mL of washing solvent, 1.2 mL of elution solvent) and exhibits excellent purification ability, with high sensitivity and accuracy, and was successfully applied for the determination of E2 in milk products.