Used primarily as an internal standard in mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. It aids in the accurate quantification of N-Acetyl-4-aminobiphenyl and related aromatic amine metabolites in biological samples such as urine and blood. Due to its deuterated structure, it provides excellent isotopic separation from the non-labeled compound, minimizing interference and enhancing measurement precision. Commonly applied in toxicological and metabolic studies to assess exposure to aromatic amines, which are known environmental carcinogens. Its stability and distinct mass signature make it ideal for pharmacokinetic studies and biomonitoring applications.