Which of the following is NOT a good sampling practice?

• A. Take several increments and composite them to form the sample.
• B. If possible, mix the material before sampling.
• C. Sample frequently enough to allow for the identification of process cycles.
• D. Collect the sample in a container made of material that will chemically react with the sample.

Answer: (D)

Maintaining sample integrity by avoiding any change to the sample during collection is the key idea. If the container or handling materials react with the sample, you can alter its composition, introduce impurities, or cause components to be added or removed. This makes the measured results unrepresentative of the actual material you’re trying to analyze, which defeats the purpose of sampling.

Using a container that will chemically react with the sample is not a good practice for this reason—it can change what you’re trying to measure, leading to biased or erroneous results. Inert or compatible materials (like certain types of glass, PTFE, or other nonreactive metals/plastics appropriate to the sample) are chosen specifically to preserve the sample’s original composition.

The other options describe sound sampling practices that help capture a true picture of the process: taking multiple increments and compositing them improves representativeness by averaging out variability; mixing the material before sampling reduces stratification and ensures a uniform sample; and sampling frequently enough to identify process cycles captures temporal changes rather than a single snapshot.