Surveillance study of novobiocin and phenylbutazone residues in raw bovine milk using liquid chromatography-tandem mass spectrometry

Abstract

A simple method permitting the simultaneous determination of trace residues of novobiocin and phenylbutazone in raw milk samples using liquid chromatography-tandem mass spectrometry was developed. Raw milk samples were mixed with acetonitrile to facilitate the concurrent precipitation of milk proteins and extraction of both veterinary drugs. Without additional clean-up or concentration of the resulting extract, the analytes could be quantified at concentrations as low as 0.0025 and 0.001 µg ml⁻¹ for phenylbutazone and novobiocin, respectively. The analysis of a series of fortified raw milk samples at analyte concentrations ranging from 0.005 to 0.1 µg ml⁻¹ and from 0.01 to 0.2 µg ml⁻¹ for phenylbutazone and novobiocin, respectively, yielded average recoveries ranging from 89.2% to 104.3% with standard deviations below 7%. The analytical method was applied to the analysis of raw milk samples collected from transport trucks upon delivery at dairy-processing plants throughout Alberta, Canada. Novobiocin was detected in 13 of 1072 samples tested at concentrations ranging from 0.001 to 0.007 µg ml⁻¹. Phenylbutazone was not detected in any of the samples tested.

Keywords:

• liquid chromatography/mass spectrometry (LC/MS)
• veterinary drug residues
• antibiotics
• veterinary drugs
• milk

Acknowledgements

The authors gratefully acknowledge the technical assistance of the staff of Agri-Food Laboratories (Joy Komarnicki, Renata Limanowka, Marlise Siegenthaler, and Desmond Tang) during completion of this study. The cooperation of John Komarnicki and his staff at the Central Milk Testing Laboratory is greatly appreciated.