What is the purpose of a spike recovery test, and how is it interpreted?

• A. To measure instrument drift over time.
• B. To determine the detection limit of the method.
• C. To calibrate the instrument using a matrix blank.
• D. To assess method accuracy in the matrix; recoveries near 80–120% indicate acceptable performance.

Answer: (D)

Spike recovery testing checks how accurate a method is in a real sample matrix by adding a known amount of analyte and seeing how much is recovered after sample preparation and analysis. You compute percent recovery as (measured amount) ÷ (amount spiked) × 100. Recoveries near 100% indicate the method is accurate in that matrix, while recoveries in the 80–120% range are generally considered acceptable, acknowledging that some matrix effects or small procedural losses are normal. If recoveries deviate significantly from this range, it suggests the matrix is influencing the measurement or the extraction/detection steps are not performing properly, signaling potential bias in the results. This approach focuses on method accuracy within the matrix, rather than instrument drift, detection limit determination, or merely calibrating with a matrix blank.