What is the required preservation and storage time for Alkalinity samples?

• A. Keep samples at room temperature; 24 hours
• B. Freeze at -20C; 7 days
• C. Store samples at 4C; 72 hours
• D. Cool <= 6C; 24h/14D

Answer: (D)

Preserving alkalinity samples centers on keeping the carbonate system from changing before analysis. Cooling slows any chemical and biological processes that could shift carbonate and bicarbonate concentrations or release CO2. Keeping the sample at about 6 C or cooler minimizes these changes, so the sample remains stable longer. In practice you should analyze within 24 hours when kept cold, and some protocols allow extending stability up to 14 days if the sample is properly preserved and sealed. The other options fail because room temperature speeds changes, freezing can disturb carbonate equilibria, and a 72-hour hold at 4 C is more restrictive than the standard 24-hour or 14-day windows.