Used as a stable isotope-labeled internal standard in mass spectrometry-based assays for the accurate quantification of N-Acetyl Folic Acid in biological samples. Its primary application is in pharmacokinetic and metabolic studies where precise measurement of folic acid derivatives is required. The deuterated form allows for differentiation from the non-labeled compound during analytical detection, minimizing interference from matrix components. It supports research in folate metabolism, especially in studies related to drug metabolism, nutritional biochemistry, and biomarker validation.