Used as a stable isotope-labeled internal standard in analytical chemistry, particularly in mass spectrometry and gas chromatography, to accurately quantify phenol and its metabolites in environmental and biological samples. Its deuterated structure allows for clear differentiation from non-labeled compounds during detection, improving measurement precision. Commonly applied in studies monitoring phenol exposure in humans, such as urine analysis in occupational health, and in environmental testing to track phenolic pollutants in water and soil. Also utilized in metabolic studies to trace phenol transformation pathways in biological systems without altering chemical behavior.