Used as a stable isotope-labeled internal standard in mass spectrometry and liquid chromatography-mass spectrometry (LC-MS) assays for quantitative analysis of acetaminophen metabolites and related compounds. Its deuterated structure allows for accurate differentiation from non-labeled analogs, improving measurement precision in pharmacokinetic and metabolic studies. Commonly applied in drug development, forensic toxicology, and biomarker validation where high analytical sensitivity and specificity are required.