Phenylthiohydantoin-arginine hydrochloride is primarily utilized in biochemical research, particularly in the field of protein sequencing. It plays a critical role in the Edman degradation process, a method used to determine the amino acid sequence of peptides and proteins. This compound is specifically involved in the identification of arginine residues within the peptide chain. Its application ensures accurate and efficient sequencing, which is essential for understanding protein structure and function. Additionally, it is used in the synthesis and modification of peptides for various scientific studies, aiding in the development of therapeutic agents and the exploration of biological pathways.