Why are collocated and duplicate samples used in QA/QC?

• A. To calibrate the instrument.
• B. To quantify precision, identify sampler bias, and verify data quality.
• C. To lower costs.
• D. To reduce sampling time.

Answer: (B)

Collocated and duplicate samples are used to check how reliable the measurement process is. When two samplers are placed at the same location for the same time, any difference between their readings helps reveal sampler bias—whether one device tends to read higher or lower than another under identical conditions. Duplicate samples, taken from the same air draw or split from the same sample, test repeatability by showing how close repeated measurements are when nothing else changes. Together, they let you quantify precision (the tightness of repeated results) and verify data quality, so you can trust the reported concentrations. This approach is about assessing measurement reliability, not about calibrating instruments, lowering costs, or speeding up sampling. If collocated results agree and duplicates are close, you have confidence in the data; if they don’t, it signals possible issues to address.