Question 4 of 6 Intermediate Scenario
How do specificity and selectivity matter for analytical methods?
Short answer
Both concern whether a procedure measures the intended analyte in the presence of other substances. The precise term and evidence depend on the analytical technique and intended use.
Why
For a biologic potency assay, a response can reflect target-specific activity, interfering matrix components or nonspecific cell stress. Design challenges with blanks, known impurities, degradation products and relevant excipients to show that the measurement remains meaningful under plausible sample conditions. In a chromatography method, demonstrate resolution of the analyte from related peaks and assess interference at concentrations relevant to release or stability testing.
Analytical characteristics are not universally interchangeable and regulatory terminology varies by method type. Select conditions based on the procedure analytical target profile and risk, then document acceptance criteria before experiments. A clean peak or strong correlation in a narrow calibration set is not sufficient evidence of specificity in real production matrices.
Common mistakes
- Assuming a well-separated reference standard proves specificity for every product matrix
The interviewer might ask next
How would you assess a newly detected degradant that coelutes with the main peak?