Used as a stable isotope-labeled internal standard in mass spectrometry and metabolic research to accurately quantify guanidine and related compounds in biological samples. Its isotopic enrichment (13C and 15N3) allows differentiation from endogenous guanidine, improving measurement precision in studies related to kidney function, diabetes, and neurodegenerative diseases. Also employed in protein labeling and tracer studies to monitor metabolic pathways and enzyme mechanisms.