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-1.  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.