Used as an internal standard in mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the quantitative analysis of sulfamethazine in biological samples. Its deuterated structure allows for accurate differentiation from non-labeled compounds, improving measurement precision in pharmacokinetic studies, residue analysis in animal tissues, and environmental monitoring of sulfonamide antibiotics. Commonly applied in veterinary drug testing and food safety laboratories to ensure compliance with regulatory limits.