Hydrindantin dihydrate is primarily used in biochemical research and analytical chemistry as a reagent for the detection and quantification of amino acids. It plays a crucial role in the ninhydrin test, where it reacts with amino acids to produce a characteristic purple color, enabling the identification and measurement of amino acid concentrations in various samples. This application is particularly valuable in protein analysis, food science, and medical diagnostics, where understanding amino acid composition is essential. Additionally, it is utilized in chromatography to visualize amino acids separated on thin-layer or paper chromatograms, aiding in research and quality control processes.