Fenbufen-d9 is primarily used as an internal standard in analytical chemistry for the quantification and detection of fenbufen and its metabolites in various biological samples. Its deuterated structure ensures minimal interference with the target analytes, making it highly reliable for accurate measurements in pharmacokinetic studies and drug metabolism research. It is particularly valuable in mass spectrometry and high-performance liquid chromatography (HPLC) applications, where precise calibration and sensitivity are critical. Additionally, it aids in understanding the metabolic pathways and excretion patterns of fenbufen in both preclinical and clinical studies.