A simple methodology based on cloud point extraction prior to HPLC-PDA analysis for tetracycline residues in food samples

A sensitive pre-concentration and determination method for tetracycline residues in food samples was developed based on cloud point extraction and HPLC-DAD analysis. Tetracycline (TC) molecule was extracted to surfactant phases of polyethylene glycol (PEG-6000) in the presence of pH 5.0 buffer and high electrolyte concentration. The samples were centrifuged in order to increase phase separation and filtered by 0.45 mu m membrane after they were diluted with mixture of methanol: water (1:1) prior to HPLC determinations. Experimental variables were examined and optimized such as pH, concentration of electrolyte and surfactant, solvents, and incubation time. HPLC determination of tetracycline in the surfactant rich phase was carried out by isocratic elution of pH 4.0 oxalate buffer; methanol; acetonitrile (70:10:20). All analysis was performed with DAD detector at 276 nm and 358 nm throughout the study. By optimization of all experimental parameters, linear ranges for both wavelengths were calculated as 30-500 ng mL(-1) and 65-800 ng mL(-1), respectively. Detection limits were 9.56 and 21.11 ng mL(-1) for two wavelengths while relative standard deviations (RSD%) were lower than 4.20% for 100 ng mL(-1) tetracycline. Finally, the developed method was applied to food samples including milk, liver and breast meat of chicken.