Used as a stable isotope-labeled internal standard in mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the accurate quantification of carazolol in biological samples. Its deuterated structure allows clear differentiation from endogenous compounds and the non-labeled drug, improving measurement precision in pharmacokinetic and metabolism studies. Commonly applied in research involving beta-blocker distribution, drug interaction, and receptor binding assays. Also utilized in forensic toxicology and doping control due to its high specificity and detection reliability.