Ultrasonic-microwave method in preparation of polypyrrole-coated magnetic particles for vitamin D extraction in milk

•Ultrasonic-microwave technique was applied to the preparation of Fe3O4 @PPy.•Vitamin D preparation time was within 15 min using 0.5 mL organic solvent.•Greater accuracy and precision was achieved in the analysis of vitamin D.

In this study, a nanocomposite of polypyrrole-coated magnetite nanoparticles (Fe3O4@PPy) was prepared by ultrasonic-microwave technique, and employed as magnetic solid-phase extraction (MSPE) sorbent for extraction of vitamin D from milk samples. The term of the synthesis by ultrasonic-microwave technique was dramatically shortened within 4 h compared to 20 h by conventional stirring-heating method. The resultant composites incorporating the π–π bonding (between PPy coating and the analytes) and magnetic separation can be applied for vitamin D analysis in complicated samples. Without saponification or protein precipitation, vitamin D2 and vitamin D3 could be captured directly from milk samples by Fe3O4@PPy, and separated by magnetic field with only 0.5 mL desorption solvent. The total preparation time was completed within 15 min. A method for the determination of vitamin D in milk samples by the Fe3O4@PPy extraction coupled with high performance liquid chromatography (HPLC) was developed. The LODs of vitamin D2 and vitamin D3, based on signal-to-noise ratio (S/N) of 3, were 0.02 ng/mL and 0.05 ng/mL respectively. The recoveries of vitamin D2 and vitamin D3 from milk samples were in the range of 71.9–90.3%, with relative standard deviations ranging between 3.6%–9.9%. The results indicated that the Fe3O4@PPy can be favorably used for the extraction of the vitamin D in milk samples.