Used as a stable isotope-labeled internal standard in mass spectrometry for the detection and quantification of guanidine and its derivatives in biological samples. Its primary application lies in metabolic research and pharmaceutical analysis, where it helps trace nitrogen pathways and study drug metabolism involving guanidine-containing compounds. Due to the 15N4 labeling, it enables accurate differentiation from non-labeled analogs during analytical testing, improving precision in quantitative assays.