Used as a stable isotope-labeled internal standard in mass spectrometry and nuclear magnetic resonance (NMR) studies to track metabolic pathways and quantify propionic acid and its derivatives in biological samples. Its deuterated form allows for clear differentiation from non-labeled compounds, improving accuracy in analytical measurements. Commonly applied in pharmaceutical research, metabolic profiling, and environmental analysis where precise detection and quantification are critical. Also employed in studies involving gut microbiota metabolism, as propionic acid is a short-chain fatty acid produced during fermentation.