Phase equilibrium and macrolide antibiotics partitioning in real water samples using a two-phase system composed of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate and an aqueous solution of an inorganic salt

An ionic liquid-salt aqueous two-phase system (ILATPS) based on the hydrophilic ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (Bmim]BF₄) and inorganic salt was developed for direct separation and analysis of macrolide antibiotics coupled with molecular fluorescence spectrophotometry. Liquid–liquid equilibria of Bmim]BF₄-salt aqueous two-phase systems were studied for different salts and temperatures. It was found that the salting-out ability of different salts may be related to the Gibbs energy of hydration of the ions, and the two-phase area was expanded with a decrease in temperature. The partition coefficients as well as extraction efficiencies of azithromycin and mydecamycin in Bmim]BF₄-salt aqueous two-phase system were influenced by the types of salts, concentration of salt, and the extracting temperature. Under the optimum conditions, the average partition coefficient of azithromycin in Bmim]BF₄-Na₂CO₃ ILATPS was 162, and that of mydecamycin in Bmim]BF₄- NaH₂PO₄ ILATPS was 90.9. This method has been satisfactorily applied to the determination of azithromycin and mydecamycin in real water samples with detection limits of 0.059 µg mL^?1 and 0.019 µg mL^?1. This extraction method is a simple, non-toxic and effective sample pretreatment technique with promise also for the separation of other small biomolecules.