In QA/QC, which item is used to detect contamination arising during sampling and handling, not during laboratory reagents?

• A. A method blank
• B. A matrix spike
• C. A field blank
• D. A standard reference material

Answer: (C)

Contamination that comes in during the field collection and handling steps is revealed by a field blank. This control goes through the same sampling process as real samples, using the same containers and handling procedures, but contains no actual sample or target analyte. If the field blank shows detectable levels, it points to contamination introduced in the field environment, from bottles, equipment, or handling, rather than from lab reagents or analysis.

In contrast, a method blank is prepared in the laboratory and checks for contamination from lab reagents or instrument carryover; a matrix spike tests recovery of analyte in a specific sample matrix to assess accuracy; a standard reference material is a known material used to verify method performance and calibration.