Used as a stable isotope-labeled internal standard in mass spectrometry and HPLC analyses for the accurate quantification of theobromine in biological samples such as blood, urine, and tissues. Its primary application is in pharmacokinetic studies, doping control, and forensic toxicology, where it helps distinguish between endogenous theobromine and exogenous sources. Due to its identical chemical properties but increased mass, it ensures precise measurement without interfering with the native compound’s behavior during analytical procedures.