The detection of vitamin D in complex samples is challenging because of the instability of vitamin D in sample preparation. To resolve this problem, packed-fiber solid-phase extraction (PFSPE) has been successfully developed for the pre-treatment of samples containing vitamin D2 (D2) and vitamin D3 (D3) in dairy products. Based on PFSPE, vitamin D could avoid oxidation because of the shorter extraction time. The adsorbent materials, polystyrene/polypyrrole (PS/PPy) nanofibers, were prepared by electrospinning of PS and in situ polymerization of PPy on the surface of PS nanofibers. The linearity was within the range of 1-2000 ng mL−1 in dairy solution, and the recoveries were 91.9-109.1% with a relative standard deviation (RSD) < 13.6%. Therefore, the prepared method could be used for the detection of D2 and D3 in dairy products.

A solid-phase extraction (SPE) method based on conductive polypyrrole (PPy) nanofibers which were fabricated by electrospinning and in situ polymerization was developed. PPy nanofibers-mediated SPE followed by high performance liquid chromatography (HPLC) was used for the determination of three synthetic estrogens, namely diethylstilbestrol (DES), dienestrol (DIS), or hexestrol (HS) in milk sample. Extraction conditions including extraction nanofibers, donor solution pH and salt concentration were optimized. The target compounds were extracted from a 0.5 mL aqueous sample at pH 5.0 through PPy fibers, and then were eluted with 0.1 mL methanol. After extraction, the eluant was directly injected into an HPLC system for detection. Under the optimized extraction conditions, a large enrichment factor was achieved for three estrogens. The limit of detection (LOD) at a signal to noise ratio (S/N) of 3 ranged from 0.02 to 0.05 µg mL-1 for the estrogens in milk sample.