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)

After an immunoassay screen, confirmation with GC-MS is used to obtain a definitive identification and precise quantification of the target drug or metabolite. Immunoassays are fast and inexpensive but can cross-react with similar substances, leading to false positives. GC-MS separates the sample components and analyzes their mass spectra, producing a unique pattern for the specific compound and its retention time that can be matched to standards. This high specificity allows labs to confirm true positives and determine exact concentrations, effectively resolving questionable results from the screening. It’s not about increasing throughput, identifying unknowns by weight alone, or replacing the initial screen; it’s about providing a confirmatory, defensible result with accurate identification and quantification.