Preparation of Fe3O4@TiO2/graphene oxide magnetic microspheres for microchip-based preconcentration of estrogens in milk and milk powder samples

We reported new magnetic microspheres as the adsorbent of estrogens. They were prepared by coating Fe3O4 particles with a composite made from titanium dioxide and graphene oxide (Fe3O4@TiO2/GO). The beads were loaded into a microfluidic chip and used to adsorb estrone (E1), estradiol (E2), and estriol (E3). The estrogens were then eluted from the beads with methanol and submitted to high performance liquid chromatography (HPLC) determination. Effects of sample volume, sample flow rate, sample pH value, and eluent flow rate were optimized. The limits of detection for estrogens were in the range of 4.3–7.5 ng mL−1, and recoveries ranged from 70.6% to 94.5%. Intra-day and inter-day relative standard deviations were less than 2.5% and 3.2%, respectively. The results indicated that the method was successfully applied to the determination of estrogens in milk and milk powder samples.