LAUSR

AbstractIonic liquid foam floatation coupled with an ionic liquid-based homogeneous liquid–liquid microextraction (IF-IHLME) method was developed and compared with ionic liquid foam floatation coupled with an ionic liquid dispersive liquid–liquid microextraction (IF-IDLME) method by their application to the extraction, separation and determination of 17-α-estradiol, 17-β-estradiol-benzoate and quinestrol in environmental water samples. Based on the unique properties of ionic liquids (ILs), the advantages of foam floatation (FF) and the homogeneous liquid–liquid microextraction (HLLME) method were applied to the IF-IHLME method. The experimental parameters of the IF-IHLME method, including the salt concentration in the sample solution, type and volume of ILs, amount of ion-pairing agent (NH4PF6) and extraction time were evaluated. The limits of detection for 17-α-estradiol, 17-β-estradiol-benzoate and quinestrol were 0.04, 0.05 and 0.05 ng mL−1, respectively. When the proposed method was applied to the analysis of water samples, the recoveries of the analytes ranged from 95.5 to 114.6%, and relative standard deviations were lower than 8.00%. By comparison, both of these two proposed separation and extraction procedures can be successfully applied to the water sample pretreatment for HPLC detection, but the enrichment factor of IF-IHLME is much higher than that of IF-IDLME, which ranged from 5334 to 5558. These two methods requiring no organic solvent and inexpensive instrumentation in the experiment process were both environmentally friendly. Different properties of ionic liquids were applied in these two methods, for example, foam and extraction, and the property of mutual transformation between the hydrophilic and hydrophobic phase was applied in the IF-IHLME method; foam, extraction and hydrophobic properties of ILs were applied in the IF-IDLME method. These two methods were similar but not the same. Based on the unique properties of ionic liquids, the application of foam floatation and liquid–liquid microextraction was widened and has many possibilities.Graphical abstract