What is a spike in quality control?

• A. A random sample collected from the field.
• B. A standard reference material used for external calibration.
• C. A duplicate of the sample used for averaging results.
• D. A known and verified mass or activity of the target analyte of interest added to reagent water or an environmental sample to determine recovery efficiency or for other quality control purposes

Answer: (D)

In quality control, a spike means adding a known amount of the target analyte to a sample before processing. This lets you measure how well the method can recover the analyte through the entire workflow, from sample prep to measurement. By comparing the amount you recover after analysis to the amount you added, you calculate recovery efficiency and assess accuracy in that specific matrix. If the recovery falls within an acceptable range, it indicates the method is performing reliably for that type of sample and helps confirm there’s no significant matrix effect or procedural bias. Spiking is a practical way to validate method performance and to identify potential issues with extraction, cleanup, or detection.

This differs from a random field sample, which is simply a real sample used for measurement rather than a QC check. It also differs from a standard reference material used for external calibration, which is about calibrating the instrument or method rather than testing how the method performs on a given sample. And it differs from creating a duplicate of the sample for averaging results, which is a replicate to assess precision rather than to test recovery.