Used as a stable isotope-labeled tracer in metabolic studies to track the citric acid cycle (Krebs cycle) in cellular respiration. Enables precise monitoring of metabolic flux in tissues, particularly in research involving energy metabolism, mitochondrial function, and cancer cell metabolism. Commonly employed in mass spectrometry and nuclear magnetic resonance (NMR) studies due to its labeled carbon positions, allowing differentiation from endogenous citric acid. Also utilized in pharmaceutical and nutritional research to study organic acid metabolism and in labeling experiments for biosynthesis pathways.