Simultaneous determination of amoxicillin and ampicillin in eggs by reversed-phase high-performance liquid chromatography with fluorescence detection using pre-column derivatization.

A sensitive and robust method is presented for the simultaneous determination of amoxicillin (AMO) and ampicillin (AMP) in eggs by reversed-phase high-performance liquid chromatography with fluorescence detection (RP-HPLC-FLD). This method used a simple liquid-liquid extraction of the samples with acetonitrile and dichloromethane as precipitation of proteins and extraction solvent. AMO and AMP reacted with salicylaldehyde to form fluorescent derivatives, which were then analyzed with RP-HPLC-FLD. Separation was carried out on an Athena C18 column with a mobile phase consisting of 0.01 M potassium dihydrogen phosphate, adjusted to pH 5.5 by 2M potassium hydroxide and acetonitrile. The detector response was linear over the tested concentration range from 5.0 to 800 ng/mL for AMO and AMP. The recovery values ranged from 78.4 to 88.7% for AMO and from 77.6 to 82.0% for AMP. The limits of detection were 1.2 for AMO and 0.4 µg/kg for AMP. The limits of quantification were 3.9 for AMO and 1.5 µg/kg for AMP. The corresponding intra-day and inter-day variation (relative standard deviation) were found to be less than 9.6 and 14.8%, respectively.