Determination and depletion of amoxicillin residues in eggs.

Eggs were used to study the determination and depletion of amoxicillin (AMO) residues after oral dosing hens (25.0 mg kg⁻¹, 50.0 mg kg⁻¹ body weight), once daily for five days. A reverse-phase high-performance liquid chromatography with fluorescence detection (RP-HPLC-FLD) method was developed to determine AMO residues in albumen, yolk and whole egg. By using pre-column derivatisation, an improved liquid-liquid extraction procedure was developed for sample preparation. AMO were extracted from eggs with acetonitrile. The extract solution was extracted using saturated methylene chloride. The supernatant was reacted with salicylaldehyde under acidic and heating conditions. Limits of detection (LODs) were 1.2 ng g⁻¹ and limits of quantification (LOQs) were 3.9 ng g⁻¹ for AMO. Recoveries of AMO from samples fortified at levels of 5.0-125.0 ng g⁻¹ ranged from 79.1% to 88.5% in albumen, 78.6-83.6% in yolk and 78.3-85.1% in whole egg, with coefficients of variation of ≤7.3%. The maximum concentrations of AMO in albumen, yolk and whole egg were found to occur at 1.5, 2.5, 1.5 days after withdrawal of medication respectively. AMO was not detectable in albumen at 7.5 days after final administration of AMO, at 10.5-11.5 days in yolk and 10.5 days in whole egg after administration of two oral doses. The method was applied during the residue study of AMO in order to formulate a reasonable withdrawal period to ensure food safety.