Water samples should not be stored for more than how long before analysis unless acidification is completed?

Water samples should not be stored for more than how long before analysis unless acidification is completed?

• A. 6 hours
• B. 12 hours
• C. 24 hours
• D. 28 hours before analysis, unless acidification is completed

Answer: (D)

Preservation and hold time are about keeping a water sample’s composition stable until it’s analyzed. For metal analyses, acidifying the sample to a low pH (usually with nitric acid) slows down biological activity and prevents changes in metal speciation or loss through precipitation or adsorption. When that acidification step is completed, the sample can be stored for up to 28 hours before analysis. If acidification hasn’t been done, the sample isn’t protected from these changes, so you’d have to analyze it sooner to ensure accurate results. The other shorter time frames wouldn’t permit the same level of stability that acidification provides.

Preservation and hold time are about keeping a water sample’s composition stable until it’s analyzed. For metal analyses, acidifying the sample to a low pH (usually with nitric acid) slows down biological activity and prevents changes in metal speciation or loss through precipitation or adsorption. When that acidification step is completed, the sample can be stored for up to 28 hours before analysis. If acidification hasn’t been done, the sample isn’t protected from these changes, so you’d have to analyze it sooner to ensure accurate results. The other shorter time frames wouldn’t permit the same level of stability that acidification provides.