Abstract:

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method has been developed for the determination of eight compounds in milk and milk powder. They are four penicillins (penicillin G, penicillin V, amoxicillin and ampicillin) and four major β-lactamase enzymatic metabolites of them (penilloic acid G, penilloic acid V, amoxiilloic acid and ampilloic acid). The compounds were extracted from the samples with acetonitrile and water, cleaned-up by HLB solid-phase extraction cartridges, and then detected by HPLC-MS/MS and quantified by external standard method. The linearities were satisfactory with the correlation coefficients >0.99 at the mass concentrations ranging from 4 μg/L to 200 μg/L for penicillins and from 10 μg/L to 500 μg/L for enzymatic metabolites. The limits of detection and the limits of quantification were 5-50 μg/kg (S/N≥3) and 8-100 μg/kg (S/N≥10), respectively. The average recoveries of the eight compounds were 83.48%-96.97% in milk and 82.70%-95.14% in milk powder. The relative standard deviations (RSDs) in milk and milk powder were 3.86%-10.87% and 3.02%-9.81%, respectively. In conclusion, the established method is convenient, accurate and sensitive so that it can be applied to the determination of penicillin residues and enzymatic metabolites in milk and milk powder.

Key words: enzymatic metabolites, high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), milk, milk powder, penicillin