Quantitative determination of ceftiofur in milk by liquid chromatography–electrospray mass spectrometry
Introduction
A number of veterinary drugs which are frequently used to prevent infections, can contaminate meat and milk products destined for human consumption. Ceftiofur (Fig. 1) is a cephalosporin β-lactam antibiotic which is finding widely increased use in the treatment of bacterial infections. While residues of ceftiofur and its metabolites have been reported in bovine milk and serum 1, 2, 3, mass spectrometry (MS) methodology has not been developed for the confirmation of this antibiotic at the 50 ppb tolerance level set by US Food and Drug Administration (FDA) [4]. Based on the presence of a basic nitrogen on ceftiofur and its polar and thermally unstable properties, electrospray positive-ion detection (analyzing ceftiofur at low pH to protonate the molecule in solution) should be feasible 5, 6. Also, ceftiofur and other antibiotics from the cephalosporin class have been analyzed by positive-ion detection electrospray mass spectrometry (ES-MS) 7, 8, 9.
To achieve the ES-MS sensitivity necessary to detect residues of ceftiofur in milk, ES-MS required the use of an Rf ion guide to improve ion transport. The Rf ion guides offer advantages over electrostatic lens systems for transmissions of ions into the mass analyzer 10, 11, 12, 13, 14, 15. Rf ion guides involving quadrupole, hexapole and octapole configurations are now commonly used in the ion transport region of the atmospheric pressure ionization (API) interface for introduction of ions into a mass analyzer.
This paper presents the research into developing a quantitative confirmation methodology based on liquid chromatography–electrospray-mass spectrometry (LC–ES-MS) for ceftiofur in milk at the 25 ppb level.
Section snippets
Materials and reagents for LC–MS analysis
Water was purified with a Milli-Q water system (Millipore, Bedford, MA, USA) prior to use. Acetonitrile (ACN) was of LC–GC grade quality (Baxter Healthcare, Muskegon, MI, USA). The ion-pair reagent, heptafluorobutyric acid (HFBA) was obtained from Aldrich (Milwaukee, WI, USA). Ceftiofur hydrochloride standard was supplied by the Upjohn (Kalamazoo, MI, USA). The FDA milk samples collected 32 and 48 h after dosing with ceftiofur were supplied by the FDA Center of Veterinary Medicine, Beltsville,
Sample preparation
The development of the method took into account the need to handle large numbers of samples. For this reason the simple and rapid procedure of ultrafiltration using a 10 000 molecular-mass cutoff filter was chosen for sample clean-up. A 100-μl aliquot of the filtrate was concentrated on column. Ultrafiltration has been previously optimized in our laboratory for the extraction of β-lactams in milk [16]. This optimization demonstrated the need of the addition of an organic solvent to the milk to
Acknowledgements
This work was supported by the Food and Drug Administration under Cooperative Agreement Number FD-U-000589. Also, the authors thank both Hewlett-Packard and Analytica of Branford for technical assistance and instrumentation used in this work.
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2019, TrAC - Trends in Analytical ChemistryQuantification techniques for important environmental contaminants in milk and dairy products
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Application of partially fluorinated carboxylic acids as ion-pairing reagents in LC/ESI-MS
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A new indirect method based on square-wave voltammetry for ceftiofur determination in bovine milk using an alkaline degradation product
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