What is the purpose of GC-MS confirmation after an immunoassay screen?

What is the purpose of GC-MS confirmation after an immunoassay screen?

• A. To increase screening throughput and reduce costs.
• B. To identify unknown compounds by molecular weight alone.
• C. To provide specific, confirmatory identification and quantification of the drug/metabolite with high specificity and to resolve false positives from screening.
• D. To replace the need for immunoassay screening.

Answer: (C)

The test concept here is that a screening immunoassay is fast and broad but can give false positives, so a highly specific confirmatory test is needed to verify identity and quantify the drug accurately. GC-MS confirmation provides that precision. By separating the sample’s components with gas chromatography and then analyzing each compound with mass spectrometry, you get a unique retention time and a detailed mass spectrum for each substance. Matching both the retention time and the characteristic fragmentation pattern to authentic standards allows definitive identification of the drug or metabolite and precise quantification. This specificity helps resolve false positives that can arise from immunoassay cross-reactivity or interference. It’s not used to increase throughput or to identify unknowns by molecular weight alone, and it doesn’t replace screening; it serves as the confirmatory step that validates and quantifies what the initial screen suggested.