Development of nitrogen-blowing salt-induced solidified floating organic droplet microextraction for determination of phenolic oestrogens in milk samples

In solidified floating organic droplet microextraction, the solidified organic phase formed a concave meniscus on the water surface, and the solidified layer was easily broken into pieces when using a medical spoon to collect it, resulting in a slow and difficult whole collection. A novel method, nitrogen-blowing salt-induced solidified floating organic droplet microextraction, was developed for pretreatment of the milk samples. After the procedures, the down layer salt and aqueous phase was discarded by opening the bottom cap. The remaining solidified solvent was easily and wholly collected by a medical spoon, resulting in a high extraction efficiency. The similarly high deprotein rate (91–96%) was obtained between using acetonitrile and without using organic solvent as precipitating agent. Under optimized conditions, the limits of detection were 0.34–0.87 μg/L, the linear range was 1–500 μg/L, the extraction recoveries were 79.2–105.2%, and the enrichment factors were 105.8–169.3 for five phenolic oestrogens.