CWEA Grade 2 Lab Analyst Practice Test

What is the preservation requirement for the pH samples before analysis?

Cool <=6 C; 7D 6h Analyze Immediately; 0.25h (15 minutes) 48H

Correct Answer:

Analyze Immediately; 0.25h (15 minutes)

Explanation:

pH is a highly time-sensitive measurement because the acidity/basicity of a water sample can change quickly after collection due to gas exchange with the atmosphere, temperature shifts, and ongoing chemical equilibria. To ensure the pH value reflects the sample as it was at collection, it should be analyzed as soon as possible, typically within about 15 minutes. Delays allow pH to drift, leading to inaccurate results, so storage or longer hold times are not acceptable for pH. Therefore, the best practice is to analyze immediately, within 0.25 hours (15 minutes).

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