Used as a stable isotope-labeled internal standard in mass spectrometry and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for accurate quantification of folic acid and its metabolites in biological samples such as blood, serum, and urine. Enables precise measurement in nutritional studies, metabolic research, and clinical diagnostics by distinguishing endogenous folic acid from the labeled compound. Also applied in pharmacokinetic studies to track absorption, distribution, and metabolism of folate in humans without altering biological activity.