Which analytical method is typically used for confirmatory drug testing after an immunoassay screen?

Which analytical method is typically used for confirmatory drug testing after an immunoassay screen?

• A. High-performance liquid chromatography (HPLC)
• B. Gas chromatography–mass spectrometry/mass spectrometry (GC-MS/MS)
• C. Enzyme-linked immunosorbent assay (ELISA)
• D. Infrared spectroscopy

Answer: (B)

After an initial immunoassay screen, you need a method that can definitively identify the exact drug and measure its amount. Immunoassays are fast and sensitive but can cross-react with similar substances, leading to false positives. Gas chromatography–mass spectrometry, especially when done in tandem, provides both separation and highly specific detection. The sample is first separated, then the mass spectrometer looks at characteristic fragmentation patterns unique to each drug. The tandem MS adds another layer of selectivity by monitoring specific ion transitions, which greatly reduces interference from other compounds. This combination yields definitive identification and accurate quantification, which is why it is the standard confirmatory test for drugs. ELISA is a screening tool, not a confirmatory method. HPLC can separate compounds but, without MS, identification is less definitive. Infrared spectroscopy generally lacks the sensitivity and specificity needed for confirmatory testing in complex biological samples.

After an initial immunoassay screen, you need a method that can definitively identify the exact drug and measure its amount. Immunoassays are fast and sensitive but can cross-react with similar substances, leading to false positives. Gas chromatography–mass spectrometry, especially when done in tandem, provides both separation and highly specific detection. The sample is first separated, then the mass spectrometer looks at characteristic fragmentation patterns unique to each drug. The tandem MS adds another layer of selectivity by monitoring specific ion transitions, which greatly reduces interference from other compounds. This combination yields definitive identification and accurate quantification, which is why it is the standard confirmatory test for drugs.

ELISA is a screening tool, not a confirmatory method. HPLC can separate compounds but, without MS, identification is less definitive. Infrared spectroscopy generally lacks the sensitivity and specificity needed for confirmatory testing in complex biological samples.