Indophenol is widely used as a redox indicator in analytical chemistry, especially in titrations involving vitamin C (ascorbic acid). It changes color from blue to colorless when reduced, making it ideal for tracking oxidation-reduction reactions. It is also employed in environmental testing to measure ammonia levels in water through colorimetric methods, where it forms a blue complex proportional to ammonia concentration. In biological studies, indophenol derivatives serve as electron acceptors in enzyme assays, helping to monitor dehydrogenase activity. Its distinct color change and sensitivity to pH and redox conditions make it valuable in lab-based diagnostics and research.