Used as a reference standard in analytical laboratories for the calibration and validation of instruments such as HPLC, UV-Vis spectrophotometers, and GC-MS. Commonly employed in environmental testing to quantify p-nitrophenol levels in water, soil, and industrial effluents. Also utilized in biochemical assays to study enzyme activity, particularly in phosphatase and nitroreductase reactions, where it serves as a substrate or reaction product. Ensures accuracy and consistency in quality control processes across pharmaceutical, agricultural, and research applications.