A determinative and confirmatory method for ceftiofur metabolite desfuroylceftiofur cysteine disulfide in bovine kidney by LC–MS/MS

Ceftiofur is a cephalosporin β-lactam antibiotic widely used for treating certain bacterial infections in beef and dairy cattle. The regulatory HPLC–UV method for ceftiofur residues in animal tissues is time consuming and non-specific. Additionally, because the regulatory method involves chemical reactions to convert the metabolites into a single moiety, it is virtually impossible to incorporate the procedure into a multi-residue method. Ceftiofur residue violations in beef and dairy cattle have been frequently reported and therefore an improved method is needed. Herein we report a rapid and sensitive LC–MS/MS method for the determination and confirmation of ceftiofur metabolite, desfuroylceftiofur cysteine disulfide (DCCD), in bovine kidney tissue. The new method utilizes a simple extraction with phosphate buffer followed by SPE cleanup. A deuterated internal standard was synthesized and used for quantitation. The matrix-based calibration curve was linear from 25 to 2000 ng/g. The average accuracy for control kidney samples from six different sources fortified at 50–1000 ng/g was 97.7–100.2% with CV ≤ 10.1%. The limit of confirmation was 50 ng/g.