Used as a stable isotope-labeled internal standard in mass spectrometry and liquid chromatography-mass spectrometry (LC-MS) assays for accurate quantification of L-methionine in biological samples such as plasma, serum, and tissues. Its deuterated methyl group allows clear differentiation from endogenous L-methionine, improving measurement precision in metabolic studies, nutritional research, and clinical diagnostics.

Also employed in tracer studies to investigate methionine metabolism, protein synthesis, and methylation processes without altering the biochemical behavior of the molecule.