Development and optimization of a thiol imidazolium-based ionic liquid for ultrasonic assisted liquid-liquid microextraction combined with HPLC-FLD for determination of bisphenols in milk and juice samples

Herein, a novel thiol imidazolium-based ionic liquid [C4MIM-SH]Br was synthesized by a facile three-step synthesis method, and its molecular structure was characterized by infrared (IR) spectra, H-1 nuclear magnetic resonance (NMR) and mass spectrometry (MS). In addition to its merits as an ionic liquid, [C4MIM-SH]Br has strong acidity and high hydrophilicity. By integrating a conventional extractant ([CnMIM]PF6) with [C4MIM-SH] Br as a disperser, a whole ionic liquid microextraction was developed for determination of bisphenols (BPs). The main factors influencing extraction efficiency were optimized by Plackett-Burman design (PBD), single factor screening and central composite design as follows: 78 mu L [C6MIM]PF6 as extraction solvent, 81 mu L [C4MIM-SH]Br as disperser, 7 min ultrasound time, 13.5 min cooling time and 3min centrifugation time at 4000 rpm. Under optimized conditions, this method gave limit of detection for bisphenols in range of 0.13-0.82 mu g L-1 in milk and juices, relative recoveries of 91.6-107.9%. Advantages of using [C4MIM-SH]Br as an independent disperser include avoiding an extra pH adjustment step, producing a rapid and clear layering phenomenon leading to convenient separation, and providing lower detection limits and higher extraction recoveries. Due to its multi-functions, [C4MIM-SH]Br has widespread application prospects in food analytical fields.