Used as a stable isotope-labeled internal standard in analytical chemistry, particularly in mass spectrometry and gas chromatography, to accurately quantify diethyl phthalate and related phthalate esters in environmental, biological, and food samples. Its deuterated structure allows for differentiation from non-labeled compounds, improving measurement precision and reliability. Commonly applied in studies monitoring phthalate exposure, metabolic research, and contamination analysis due to its resistance to isotopic fractionation during sample preparation and analysis.