Hexafluoroisopropanol-induced salt-free catanionic surfactant coacervate extraction method for determination of fluoroquinolones in milk samples

Coacervation and phase separation were first reported in salt-free catanionic surfactant aqueous systems based on lauric acid (LA) and dodecyltrimethylammonium hydroxide (DTAOH), using hexafluoroisopropanol (HFIP) as a coacervate-inducing agent. The liquid–liquid two-phase separation occurs over a wide of LA/DTAOH molar ratios (78:22–0:100   mol/mol) and total surfactant concentrations (5–200   mmol   L −1 ) upon adding a small amount of HFIP (<10%, v/v). HFIP-induced salt-free LA/DTAOH catanionic surfactant system has much wider two-phase region than HFIP-induced salt-containing sodium laurate/dodecyltrimethylammonium bromide system. A HFIP-induced LA/DTAOH coacervate extraction method was established and coupled to high-performance liquid chromatography-ultraviolet detector (HPLC-UV) for determination of fluoroquinolones (rufloxacin, ciprofloxacin, danofloxacin, enrofloxacin) in milk. Detection limits are from 0.3   ng   mL −1 to 1.4   ng   mL −1 . Intra- and inter-day precisions (n   =   6) are in range of 4.5–8.3% and 5.8–10.7%, respectively. Recoveries are from 87.8% to 109.0%. The method, HFIP-induced salt-free coacervate extraction with HPLC-UV, is suitable for detecting trace fluoroquinolones in milk.