Used as a stable isotope-labeled tracer in metabolic studies to track glutamine metabolism in cells, particularly in cancer research and immunology. Enables precise measurement of metabolic fluxes in pathways such as the citric acid cycle and amino acid biosynthesis. Commonly applied in mass spectrometry and nuclear magnetic resonance (NMR) experiments for quantitative analysis of metabolic activity in biological systems. Also utilized in cell culture media to study protein synthesis and nitrogen metabolism without introducing natural abundance isotope interference.