Questions: Analytical Method Validation

Question 1

An analyst runs the same certified reference sample 10 times and gets highly consistent results, but the mean measured value is 15% above the certified value. Which combination of validation parameters does this describe?

• A. High precision and high accuracy
• B. High precision and low accuracy
• C. Low precision and high accuracy
• D. Low precision and low accuracy

Answer: (B)

Precision measures reproducibility — how tightly repeated measurements cluster together. High consistency across 10 replicates means high precision. Accuracy measures how close the mean result is to the true value. A systematic 15% positive bias means the method is inaccurate even though it is precise. These two properties are independent: a precise method can be systematically wrong (a calibrated but biased instrument), and an accurate method can have high variability.

Question 2

The limit of detection (LOD) and the limit of quantitation (LOQ) are identical — both define the lowest concentration an instrument can reliably measure.

• T. True
• F. False

Answer: False

LOD and LOQ are distinct thresholds. LOD is the lowest concentration at which an analyte can be distinguished from background noise with a defined confidence level (conventionally 3σ above the blank signal). LOQ is the lowest concentration that can be quantitated with acceptable precision and accuracy (conventionally 10σ above the blank signal). Because LOQ requires reliable measurement rather than mere detection, LOQ > LOD. A signal at the LOD tells you the analyte is present; it does not tell you how much.

Question 3

Why is robustness testing a required step in method validation rather than an optional finishing touch?

Model answer: Robustness testing deliberately introduces small, realistic variations in method parameters (pH, temperature, mobile phase composition, flow rate, column lot) and measures whether results remain within acceptable limits. It identifies which parameters are critical — meaning their variation significantly affects the outcome — so the SOP can specify tight control windows for those parameters. Without this, a method may pass validation under ideal lab conditions but fail in routine use when small, uncontrolled variations inevitably occur.

ICH Q2(R1) explicitly includes robustness as a validation parameter. Its purpose is prospective risk identification: find the weaknesses before transferring the method to a different lab or analyst. A robust method has narrow failure modes that are documented and controlled; a method that skipped robustness testing may have undiscovered failure modes.