Magnetic polyimide nanosheet microspheres for trace analysis of estrogens in aqueous samples by magnetic solid-phase extraction-gas chromatography–mass spectrometry

•Magnetic polyimide nanosheet microsphere (PI-NM/Fe3O4) composite was prepared.•PI-NM/Fe3O4 had large specific surface area (71.53 m2/g) and ferromagnetism.•PI-NM/Fe3O4 was used as the MSPE adsorbent for the first time.•Extraction equilibrium was achieved basically within 1 min for selected estrogens.•MSPE/GC-MS was successfully applied to analyze trace estrogens in aqueous samples.