Used as a stable isotope-labeled internal standard in mass spectrometry (MS) and liquid chromatography-mass spectrometry (LC-MS) analyses for the accurate quantification of diethylstilbestrol (DES) in biological samples, environmental matrices, and pharmaceutical formulations. Its deuterated structure allows for clear differentiation from endogenous DES, minimizing interference from matrix effects and improving measurement precision. Commonly applied in pharmacokinetic studies, doping control in veterinary and sports medicine, and monitoring of estrogenic contaminants in water and food samples. The methanol solution format ensures ready solubility and ease of use in automated sample preparation workflows.