9-Anthryldiazomethane is primarily used as a derivatization agent in analytical chemistry, particularly for the detection and quantification of carboxylic acids. It reacts with carboxylic acids to form stable, fluorescent derivatives, which can be easily analyzed using high-performance liquid chromatography (HPLC) coupled with fluorescence detection. This application is especially valuable in the analysis of fatty acids, amino acids, and other organic acids in complex biological samples, such as blood, urine, and tissues. Its high sensitivity and selectivity make it a useful tool in metabolomics, clinical diagnostics, and environmental analysis. Additionally, it is employed in the study of lipid metabolism and the identification of biomarkers in various diseases.