Used as a reference standard in analytical laboratories for the calibration and validation of instruments such as spectrophotometers and HPLC systems. Commonly employed in environmental testing to quantify nitrophenol levels in water, soil, and industrial effluents. Also utilized in biochemical assays to study enzyme activity, particularly in phosphatase and peroxidase reactions where p-nitrophenol acts as a detectable product. Ensures accuracy and consistency in quality control processes across pharmaceutical, agricultural, and research industries.