What is the purpose of a Proficiency Testing Sample?

• A. To calibrate instruments.
• B. To evaluate lab performance by having the composition unknown to the lab and the analyst.
• C. To replace the reference material.
• D. To test instrument drift with known values.

Answer: (B)

Proficiency testing samples are used to measure how well a lab performs its routine analyses under real-world conditions. The key idea is that the composition is unknown to both the lab and the analyst, so they can’t tailor their approach to the sample. The lab processes the sample as usual and reports results, and the proficiency testing provider compares those results to a reference value or to results from many labs. This assesses overall accuracy and consistency across the lab’s workflow, from sample handling to data reporting, and helps reveal any biases or procedural weaknesses. It also supports accreditation by showing the lab can produce reliable results on unknown samples.

These samples aren’t meant to calibrate instruments, replace certified reference materials, or test instrument drift using known values. Calibration uses known standards to adjust instrument response; reference materials verify method accuracy with known values, while drift tests monitor stability over time with known quantities. Proficiency testing focuses on the lab’s ability to obtain correct results on unknown samples.