Used as a stable isotope-labeled internal standard in mass spectrometry and HPLC-MS/MS assays for the accurate quantification of homovanillic acid in biological samples such as urine, plasma, and cerebrospinal fluid. Its primary application is in clinical and research laboratories for diagnosing and monitoring neuroblastoma and other neurological disorders where dopamine metabolism is altered. The deuterium-labeled structure provides a distinct mass difference, allowing clear differentiation from endogenous homovanillic acid, improving measurement precision and reliability. Also employed in metabolic studies to track dopamine turnover and catecholamine pathways without altering the chemical behavior of the compound.