What is the preservation for Nitrate + Nitrite?

• A. Add H2SO4 to pH<2; Cool <=6C; 1-2D/28D
• B. No preservation; 14 days
• C. Analyze ASAP; 7 days
• D. Cool; 6C; 28D

Answer: (A)

Preserving nitrate plus nitrite requires stopping biological activity and slowing chemical changes that can alter the measured concentrations. Acidifying the sample to a pH below 2 with sulfuric acid suppresses microbial processes that could convert nitrate or nitrite, and keeping the sample cool (at or below 6°C) slows any remaining reactions. When these two steps are done together, the sample can be held for a relatively long period before analysis—in many standard methods, up to 28 days.

This is why the option describing acidification to pH < 2 with H2SO4, refrigeration to ≤6°C, and a holding time up to 28 days is the best choice. Other options either miss the preservative step, omit cooling, or specify shorter hold times that don’t protect the integrity of nitrate and nitrite as effectively.