How long should water samples be stored before analysis if acidification is not completed?

How long should water samples be stored before analysis if acidification is not completed?

• A. 24 hours before analysis
• B. 12 hours
• C. 72 hours
• D. 28 hours before analysis, unless acidification is completed

Answer: (D)

Preserving water samples for metal analysis depends on whether the sample is acidified. If acidification isn’t done, the dissolved metals can still change in the bottle due to microbial activity, adsorption to the container walls, or precipitation as hydroxides. Those changes can alter the measured concentration, so the sample must be analyzed within a limited hold time. In this scenario, the maximum time you should wait before analysis is 28 hours when acidification has not been completed. The idea is to minimize any alteration of the sample’s chemistry before measurement. If acidification has been completed, the sample’s stability improves and the hold time can be longer, but for an unacidified sample, 28 hours is the standard limit. The other options don’t reflect this preservation constraint: they either cut the window shorter or extend it beyond what unacidified samples allow.

Preserving water samples for metal analysis depends on whether the sample is acidified. If acidification isn’t done, the dissolved metals can still change in the bottle due to microbial activity, adsorption to the container walls, or precipitation as hydroxides. Those changes can alter the measured concentration, so the sample must be analyzed within a limited hold time.

In this scenario, the maximum time you should wait before analysis is 28 hours when acidification has not been completed. The idea is to minimize any alteration of the sample’s chemistry before measurement. If acidification has been completed, the sample’s stability improves and the hold time can be longer, but for an unacidified sample, 28 hours is the standard limit. The other options don’t reflect this preservation constraint: they either cut the window shorter or extend it beyond what unacidified samples allow.