Dabsyl-L-tryptophan is a dabsylated derivative of L-tryptophan, commonly used as an internal standard in high-performance liquid chromatography (HPLC) for the detection and quantification of amino acids. The dabsyl group provides strong UV-visible absorbance at approximately 436 nm, enabling sensitive and specific analysis in complex biological samples like plasma, urine, or tissue extracts. This enhances the accuracy of amino acid profiling in clinical diagnostics, nutritional studies, and metabolic research. Additionally, it is utilized in peptide and protein investigations to assess tryptophan residues and their modifications, supporting structural and functional analyses.