Stability study of selected veterinary drug residues spiked into extracts from different food commodities

Abstract

Analyte stability is more commonly a confounding factor in analytical chemistry than many analysts recognize. In this study, we assessed the stability of 31 common veterinary drugs in water and final extracts of bovine (milk and kidney/liver) and chicken (muscle and egg) matrices. Two different sample preparation methods were evaluated for one-month storage of the final extracts at typical room, refrigerator, and freezer temperatures. Liquid chromatography – mass spectrometry (LC-MS) by triple quadrupole and high-resolution techniques was used for analysis of the extracts spiked at different relevant concentrations for general regulatory purposes (10–1000 ng/g sample equivalent). Comparison of results between two labs demonstrated that stable drugs (≤20% loss) at all tested conditions consisted of danofloxacin, enrofloxacin, florfenicol, flubendazole, hydroxy-flubendazole, flumequine, flunixin, 5-hydroxy-flunixin, lincomycin, and meloxicam. The tested drugs found to be the most unstable (>20% loss at room temperature within a matter of days) consisted of the β-lactams (ampicillin, cefalexin, cloxacillin, and penicillin G). Curiously, the following antibiotics (mostly macrolides) were apparently more stable in sample extracts than water: emamectin, erythromycin, ivermectin, lasalocid, monensin, tilmicosin, tulathromycin, and tylosin. Those and the other drug analytes (ciprofloxacin, doxycycline, florfenicol amine, 2-amino-flubendazole, oxytetracycline, sulfadiazine, sulfadimethoxine, sulfamethazine, and trimethoprim) were mostly stable for a month in refrigerated extracts, especially at higher concentrations, but not in all cases. In practice, freezer storage of extract solutions was found to be acceptable for at least a month, with a few exceptions.

Keywords:

• Veterinary drugs
• residue analysis
• analyte stability
• bovine and chicken tissues
• milk
• eggs

Acknowledgements

The authors wish to thank the other members of the North American Chemical Residue Working Group (Anton Kaufmann, Sherri Turnipseed, Jian Wang, Alejandra Rodríguez-Haralambides, Jon Wong, and JoMarie Cook) for our many discussions about veterinary drug residue analysis and interlaboratory study collaborations.

Disclaimer

The use of trade, firm, or corporation names does not constitute an official endorsement or approval by the USDA or ANSES of any product or service to the exclusion of others that may be suitable.

Disclosure statement

No potential conflict of interest was reported by the authors.