Sitagliptin-d4 phosphate is primarily used in research and development as a labeled internal standard in analytical chemistry. It aids in the quantification and identification of sitagliptin and its metabolites in biological samples through techniques like liquid chromatography-mass spectrometry (LC-MS). This compound is particularly valuable in pharmacokinetic studies, helping to understand drug absorption, distribution, metabolism, and excretion. Its deuterated structure ensures minimal interference with the analysis, providing accurate and reliable results. Additionally, it supports the development and validation of bioanalytical methods for therapeutic drug monitoring and clinical studies.