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

Magnetic polyimide nanosheet microspheres (PI-NMs) were used for magnetic solid-phase extraction (MSPE) for the first time. The PI-NMs were modified with magnetic Fe3O4 nanoparticles by chemical coprecipitation to produce the PI-NM/Fe3O4 composite. The prepared composite possessed a nanosheet structure, large specific surface area (71.5 m2/g), high saturation magnetization (19.1 emu/g), large adsorption capacity (≥ 676 ng/mg for selected estrogens), and good extraction stability (> 10 times). Trace estrogens in environmental water and urine samples were extracted by the PI-NM/Fe3O4 composite, desorbed, derivatized, and analyzed by gas chromatography-mass spectrometry (GC-MS). The derivatization, extraction, and desorption conditions were optimized. Extraction equilibrium was achieved within 1 min due to the good dispersibility and large specific surface area of the PI-NM/Fe3O4 composite. Under the optimized conditions, the MSPE/GC-MS method validation results showed wide linearity (0.02-50 µg/L or 0.05-50 µg/L), high determination coefficients (R2 ≥ 0.9983), good intraday and interday precisions (expressed as relative standard deviation, RSDs ≤ 8.2%), and low limits of detection (LODs, 0.001-0.015 µg/L). For the real environmental water and urine samples, the recoveries and RSDs were 77.0-112.5% and 0.1-10.7%, respectively. The performance of the MSPE/GC-MS method proved that the PI-NM/Fe3O4 composite was a good alternative material for the extraction of organic pollutants in aqueous samples.