Used as an internal standard in mass spectrometry for the accurate quantification of enrofloxacin in biological samples such as animal tissues, plasma, and milk. Its deuterated structure allows differentiation from non-labeled enrofloxacin during analysis, improving measurement precision in pharmacokinetic studies, residue monitoring, and veterinary drug testing. Commonly applied in food safety and regulatory laboratories to ensure compliance with antibiotic residue limits in edible products.