What constitutes an acceptable 'field duplicate' sample?

• A. A second wipe sample from a significantly different surface to check variability.
• B. A second wipe sample from the same exact spot.
• C. A second wipe sample from a similar surface area near the original surface to assess sampling precision.
• D. A duplicate air sample collected in addition to the surface wipe.

Answer: (C)

Field duplicate is a quality control step to evaluate how repeatable the wipe sampling method is in the field. The goal is to get an independent second wipe from a surface area that is similar and close to the original spot. This proximity keeps the surface type and contamination characteristics essentially the same, so any difference in results reflects sampling precision or method variability, not a real difference in contamination.

If the second wipe came from a very different surface, you’d be measuring variability between surfaces rather than the precision of the sampling process. If you took the second wipe from the exact same spot, there’d be little independent data to assess precision and you risk disturbing or biasing the first sample. A duplicate air sample tackles a different medium and isn’t addressing wipe sampling precision. So, the acceptable field duplicate is a second wipe from a nearby, similar surface area to assess sampling precision.