Homogenous liquid-liquid extraction followed by dispersive liquid-liquid microextraction for the extraction of some antibiotics from milk samples before their determination by HPLC

In current study, an efficient sample pretreatment method based on combination of salt induced-homogenous liquid-liquid extraction and ternary deep eutectic solvent-based dispersive liquid-liquid microextraction has been developed for the extraction of some antibiotics (oxytetracycline, doxycycline, penicillin G, and chloramphenicol) from milk samples before their analysis with high performance liquid chromatography. In this process, acetonitrile which acts as proteins precipitation agent and extraction/dispersive solvent, simultaneously, is added to the sample containing the analytes. After centrifugation, a homogenous solution (aqueous phase + acetonitrile) is formed upper the precipitated proteins of milk. This solution is passed through a barrel filled with solid sodium sulfate. By doing so, phase separation is occurred and the analytes are extracted into the separated acetonitrile phase which is subsequently taken, mixed with a newly synthesized water-immiscible deep eutectic solvent (phosphocholine chloride:dichloroacetic acid:dodecanoic acid) at mu L-level, and hastily injected into deionized water placed into a test tube. After centrifugation, an aliquat of the sedimented phase is removed and injected into the separation system. The method was validated it was found that it had high extraction recoveries (65-81%) and enrichment factors (455-567), low limits of detection (2.0-2.8 mu g L-1) and quantification (6.5-9.3 mu g L-1), and satisfactory repeatability (relative standard deviation <= 8.0%). Finally, the introduced method was utilized in analysis of the studied antibiotics in packed milk samples marketed in Tabriz, Iran.