Development of an analytical method for the analysis of diflubenzuron in whole blood, plasma, and serum using liquid chromatography tandem mass spectrometry

The integration of free-range beef livestock into the human food chain has been continuously threatened by outbreaks of babesiosis, which is propagated by ticks that vector the protozoans that cause the disease. The protozoans are spread among livestock by certain species of ticks, known collectively as cattle fever ticks (CFT). Although eliminated from the US in the 1940s, CFT continue to infiltrate the US by crossing the US/Mexico border on stray livestock and wildlife, and infest cattle herds. Orally administered acaricides are part of the strategy to control CFT. Parallel dosing studies, utilizing oral administration of the benzoylphenyl urea (BPU) compound diflubenzuron (DFB), were conducted in cattle and white tailed deer (WTD). We developed and validated a sensitive (<1 ppb) liquid chromatography/ tandem mass spectrometry (LC-MS/MS) method for DFB quantification in toxicology specimens. In fit-for-purpose testing, the method demonstrated accuracies within ±9 % of QC targets, and coefficient of variation percentages (%CV) of 14.8 % for whole blood, 9.0 % for plasma, and 8.7 % for serum. This work outlines the extraction and instrumental method for DFB analysis in these matrices. LC-MS/MS had not previously been used to detect and quantify DFB in whole blood, plasma, or serum. This is also the first method to employ carbon-13 labeled DFB (¹³C₆) as an internal standard for measuring DFB in blood matrices from bovine dosing studies.