Used as a stable isotope-labeled internal standard in analytical chemistry, particularly in gas chromatography-mass spectrometry (GC-MS) for quantifying naphthalene and related polycyclic aromatic hydrocarbons (PAHs) in environmental and biological samples. Its deuterated structure allows clear differentiation from non-labeled compounds during detection, improving accuracy and sensitivity in trace analysis. Commonly applied in studies of air pollution, metabolic pathways, and contamination monitoring where precise measurement of PAHs is critical.