Used primarily as a substrate in enzymatic assays, particularly for detecting alkaline phosphatase activity. It is commonly employed in biochemical research and diagnostic applications to measure enzyme activity in biological samples. When hydrolyzed by alkaline phosphatase, it produces phenolphthalein, which can be quantified spectrophotometrically, making it a valuable tool in laboratory settings for studying enzyme kinetics and cellular processes. Additionally, it is utilized in histochemistry for visualizing alkaline phosphatase in tissue samples, aiding in the study of enzyme distribution and activity in biological systems.