Gas chromatography coupled with mass spectrometric detection (GC-MS) provides a sensitive and selective method for determining nonylphenols and their ethoxylates in soil. Samples are typically extracted using solvent extraction or solid-phase extraction (SPE), followed by cleanup steps such as silica gel or florisil column purification to remove interferences. Prior to analysis, derivatization—commonly using silylation reagents—is performed to increase volatility and thermal stability of the analytes. A non-polar capillary GC column allows efficient separation of NP, NP1EO, and NP2EO, while the mass spectrometer provides compound identification and quantification through characteristic ion fragments and selected ion monitoring (SIM). Calibration with internal standards and the use of quality control samples ensure accuracy, precision, and reproducibility. Overall, GC-MS enables reliable and confirmatory analysis of nonylphenolic compounds in soil for environmental assessment and regulatory compliance.