Used as a stable isotope-labeled internal standard in mass spectrometry and metabolic studies to accurately quantify thiamine (vitamin B1) and its metabolites in biological samples such as blood, urine, and tissues. Its isotopic labeling allows for precise tracking of thiamine uptake, conversion, and turnover in metabolic pathways, particularly in studies related to energy metabolism, neurological function, and vitamin deficiency disorders. Also employed in pharmacokinetic research to assess absorption, distribution, and bioavailability of thiamine from dietary sources or supplements without interference from endogenous compounds.