Used as a stable isotope-labeled internal standard in mass spectrometry for quantifying trimethylamine N-oxide (TMAO) in biological samples. Enables accurate detection and measurement of TMAO levels in studies related to cardiovascular disease, kidney function, and gut microbiome metabolism. Its deuterated form ensures minimal interference from endogenous compounds, providing high sensitivity and precision in analytical workflows. Commonly applied in clinical diagnostics, metabolomics research, and pharmaceutical development.