1,2-Dichlorobenzene-d4 is primarily used as a deuterated internal standard in analytical chemistry, particularly in techniques such as NMR (Nuclear Magnetic Resonance) spectroscopy and GC-MS (Gas Chromatography-Mass Spectrometry). The replacement of hydrogen with deuterium enables precise tracking and analysis in complex samples without background interference. It is also utilized in research and development, including pharmaceutical and environmental studies, to investigate reaction mechanisms, molecular structures, chemical degradation, and migration in various systems. Additionally, it serves as a reference for calibrating instruments and ensuring accurate measurements in industrial and environmental testing.