In QA/QC, what is the purpose of collocated sampling?

• A. Collocated sampling helps determine measurement precision by comparing two instruments at the same site
• B. Collocated sampling is used to set sampling location
• C. Collocated sampling is used to calibrate equipment automatically
• D. Collocated sampling is optional in QA/QC

Answer: (A)

Collocated sampling is about checking how repeatable measurements are when two instruments run side by side at the same place and time. By directly comparing their readings under identical conditions, you can estimate the measurement system’s precision—the random variability in results. If both instruments track each other closely, the precision is high; if they diverge, there’s greater variability or potential instrument issues to address.

This approach isn’t about choosing where to take samples or automatically calibrating equipment. Calibration uses standard references or calibration procedures, and sampling location is set by the study plan. Collocation is a QA/QC check to confirm that the data are consistent and trustworthy by evaluating how closely instruments agree under the same conditions.