[Simultaneous determination of penicillin and their major enzymatic metabolites in milk and milk powder by high performance liquid chromatography-tandem mass spectrometry].

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.