Anilazine-d4 is primarily used as an internal standard in analytical chemistry, particularly in mass spectrometry and nuclear magnetic resonance (NMR) studies. Its deuterated form allows for precise quantification and tracking of anilazine and its metabolites in complex biological or environmental samples. This application is crucial in pesticide residue analysis, enabling researchers to monitor and assess the presence and degradation of anilazine in agricultural products, soil, and water systems. Additionally, it aids in pharmacokinetic studies to understand the behavior and distribution of anilazine in living organisms, contributing to safer and more effective pesticide use.