The effect of storage at 4°C on the stability of ampicillin residues in raw milk

Raw milk samples collected from tanker trucks are routinely screened for beta-lactam antibiotic drug residues using rapid screening tests. If drug residues are detected, the milk may be shipped on ice blocks to a laboratory for further analysis. A study was conducted to determine the stability of ampicillin in raw milk stored at +4 degrees C in order to predict if shipping the milk would result in the degradation of ampicillin residues. Milk samples were spiked with 20 ppb ampicillin, stored at +4 degrees C and -70 degrees C for 1-6 days, and then analysed by HPLC with fluorescence detection. No loss of ampicillin residues was found in milk stored at +4 degrees C for 1-6 days.