Salting-Out Assisted Liquid/Liquid Extraction Coupled with Low-Temperature Purification for Analysis of Endocrine-Disrupting Chemicals in Milk and Infant Formula by Ultra High Performance Liquid Chromatography-Tandem Mass Spectrometry

Abstract

In this paper, salting-out assisted liquid–liquid extraction was coupled with low-temperature purification for the analysis of five kinds of endocrine-disrupting chemicals (EDCs) in milk and infant formula by ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Acetonitrile and potassium hydrogen phosphate were used for the extraction of EDCs and the precipitation of protein. After the extract’s being frozen at −35 °C in the freezer for 2 h to remove fat, the remaining liquid phase was passed through a neutral alumina cartridge for further purification. Some important parameters, such as the extraction solvent and protein precipitant, the species and amount of salting-out reagent, the volume ratio between sample solution and acetonitrile, the freezing temperature and freezing time, as well as the amount of adsorbent, were carefully investigated and optimized to achieve the best extraction efficiency. Under the optimal conditions, good linearity was obtained with coefficient of determination ≥0.9995 except for 17β-estradiol (R 2 = 0.9950). Satisfactory recoveries were obtained for the five EDCs in the range of 73.5–119.2 %. Limits of detection were in the range of 0.03–0.23 ng mL−1. Relative standard deviations for intraday and interday precision were in the range of 4.5–9.0 and 2.7–6.0 %, respectively. The proposed method has been successfully applied to the analysis of seven kinds of market-purchased milk and two kinds of infant formula.