Drug Testing Laboratory Practice Test

In confirmatory drug testing, the goal is to definitively identify the exact substance present, not just flag a potential one. Gas Chromatography-Mass Spectrometry does this by combining separation with precise identification. Gas chromatography separates the mixture so each compound exits the column at its own retention time. When a compound elutes, the mass spectrometer ionizes the molecules and measures the resulting fragments to produce a mass spectrum—a unique fingerprint for that substance. By matching both the retention time and the mass spectrum to validated reference data, the lab can confirm exactly what substance is there and quantify it if needed. Immunoassays are excellent for rapid screening, but they can react with related substances and give false positives or negatives, so they’re not used for definitive identification. NMR spectroscopy can identify chemical structures very accurately, but it is expensive, less practical for high-throughput routine testing, and often requires purer samples. Infrared spectroscopy provides information about functional groups, but in complex biological specimens its spectra can be crowded and less definitive for distinguishing closely related drugs.