Application of magnetic ionic liquid-based air–assisted liquid–liquid microextraction followed by back-extraction optimized with centroid composite design for the extraction of antibiotics from milk samples prior to their determination by HPLC–DAD

Abstract

This research aims to suggest a magnetic ionic liquid-based air–assisted liquid–liquid microextraction procedure for preconcentration of seven multiclass antibiotics (doxycycline, tetracycline, oxytetracycline, penicillin G, chloramphenicol, ciprofloxacin, and enrofloxacin) before their determination by high performance liquid chromatography equipped with diode array detector. In the extraction process, firstly, the proteins of milk sample were precipitated using zinc acetate solution and the obtained supernatant was transferred into a glass test tube. After that, 100 µL of 1–butyl–3–methylimidazolium tetrachloroferrate ionic liquid (as an extraction solvent) was added to the solution and the resulted mixture was sucked into a glass syringe and pushed out for four times. By doing so, the cloudy state was obtained and the analytes were extracted into the produced fine droplets of the magnetic solvent. This solvent was sedimented at the bottom of the tube with the aid of an external magnet and after back–extraction of the analytes into 15 μL of a mixture of methanol, acetonitrile, and deionized water containing 0.2% formic acid (16.6, 16.6, and 66.6, v/v/v). Then, the extractant was injected into the separation system. Good analytical results such as wide linear ranges, high enrichment factors (526–606) and extraction recoveries (79–91%), and low limits of detection (0.09–0.21 ng mL−1) and quantification (0.29–0.71 ng mL−1) were obtained under the best experimental situations. Finally, the introduced procedure was employed for the quantification of the selected antibiotics in various milk samples marketed in Tabriz city (Iran).