A metal-organic framework of type MIL-101(Cr) for emulsification-assisted micro-solid-phase extraction prior to UHPLC-MS/MS analysis of polar estrogens.

A seamless two-step extraction procedure integrating ultrasound-assisted emulsification microextraction (USAEME) and vortex-assisted micro-solid-phase extraction (μ-SPE) was developed. A highly porous metal-organic framework of type MIL-101(Cr) is used as the sorbent, and ultra-high-performance liquid chromatography in combination with tandem mass spectrometry is used for detection. The steroid hormones estrone 17β-estradiol, estriol, and 17α-ethynylestradiol were extracted from water samples by using this method. These steroids are polar and do not pass through the polypropylene membrane that is conventionally used in μ-SPE. In the method presented here, 1-octanol is used in USAEME to extract and pre-concentrate the steroids. This facilitates the transfer to the MIL-101(Cr) phase retained by the membrane in the subsequent μ-SPE step. MIL-101(Cr) was characterized by various methods, and the parameters affecting the overall extraction efficiency were optimized. Under the most favorable conditions, the limits of detection are between 0.95 and 23 ng L. Good intra-day and inter-day precisions were obtained, with relative standard deviations of ≤ 9.9%. Enrichment factors are between 34 and 52. The method was applied to genuine environmental water samples in which estrone was detected. Relative recoveries ranged between 85.4% and 120.8%. Graphical abstract Schematic of the emulsification-assisted micro-solid-phase extraction (μ-SPE). By emulsifying 1-octanol in the water sample, polar estrogens dissolved in the solvent can easily pass the hydrophobic polypropylene membrane and then are adsorbed onto the unmodified MIL-101(Cr) held within the μ-SPE device.