Application of cloud point extraction for residues of chloramphenicol and amoxicillin in milk samples by HPLC–DAD

A pre-concentration and sensitive determination method for residues of Chloramphenicol (CLP) and Amoxicillin (AMX)in milk samples were developed based on cloud point extraction (CPE) and HPLC–DAD analysis. CLP and AMX moleculeswere extracted to surfactant phases of polyethylene glycol-6000 (PEG-6000) in the presence of pH 7.0 buffer andhigh electrolyte concentration. Experimental variables were examined and optimized such as concentration of electrolyteand surfactant, pH, incubation time, and diluting solvent. In the developed method, determination of CLP and AMX usingHPLC system was carried out by isocratic elution of water:acetonitrile (30:70) mixture. CLP and AMX antibiotic molecules were analyzed by considering peak area obtained by DAD detector at 273 nm and 276 nm, respectively. After optimizationexperimental variables, analytical signals were linear in the range of 10–900 ng mL− 1 and 25–1000 ng mL−1, respectively.The limit of detection values was calculated as 2.98 and 7.46 ng mL−1 while relative standard deviations (RSD %) were lowerthan 4.20% for 100 ng mL−1. Finally, the developed method was successively applied to cow milk samples.