If mechanical devices are used to agitate the sample, limit agitation to a maximum of 20 minutes.

• A. True
• B. 60 minutes
• C. 15 minutes
• D. False

Answer: (D)

When using a mechanical mixer to agitate a sample, the time spent mixing is kept short to prevent altering the sample or the test outcome. The standard practice is to cap agitation at a brief interval, typically 15 minutes. Extending agitation to 20 minutes can start to affect the sample—heating from the mixer, solvent loss, or over-mixing can bias results and reduce reproducibility. A much longer time, like 60 minutes, would be far beyond what is needed and would clearly skew the test. So the statement isn’t correct; the recommended limit is 15 minutes.