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

•Coacervation and phase separation in salt-free catanionic surfactant system.•HFIP-induced salt-free system is superior to salt-containing one in coacervation.•HFIP-induced salt-free coacervate extraction (salt-free CAE) is simple and rapid.•Salt-free CAE gave much higher enrichment factor for FQs than salt-containing one.•Salt-free CAE with HPLC-UV was used for detection of FQs in 13 kinds of milk.

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.

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