CWEA Grade 2 Lab Analyst Practice Test

Matrix spike testing checks how well your method recovers a known amount of analyte added to a sample with a complex matrix. A matrix spike duplicate means you take a second portion of the same sample, add the same known amount (the spike), and run it in duplicate. This setup lets you measure both recovery (accuracy) and precision of the spike results, because you can compare how close the recoveries are between the two spikes. If the recoveries are similar across the duplicates, you have good precision in your spike measurements and a reliable indication of method performance in that matrix. If they vary, you’re seeing variability in the spike recovery, which points to limited precision even if the average recovery looks acceptable.

In contrast, a single matrix spike focuses on recovery in one instance, which tells you about accuracy but not how reproducible the spike recovery is. A blank checks contamination or interference, and a standard reference material is used for calibration.