In GC-MS, which component is responsible for identification and quantification of the drug?

• A. GC
• B. MS
• C. GC-MS
• D. Spectrometry

Answer: (B)

Mass spectrometry provides identification and quantification in GC-MS. After a compound is separated by GC, it is ionized and fragmented, and the mass spectrometer analyzes these fragments to produce a mass spectrum that serves as a unique fingerprint for identification—often by comparing to reference libraries. For quantification, the instrument measures the intensity of chosen ions, and these signal strengths are related to concentration through calibration curves. The gas chromatography step only separates components and provides retention time; it does not by itself identify or accurately quantify a substance. The GC-MS setup combines separation with spectral data, but the component that does the identification and quantification work is the mass spectrometer. Monitoring specific ions (selected ion monitoring) can further improve the accuracy and sensitivity of drug quantification.