Which chemical is often used to preserve acidity in a water sample for testing?

Sulfuric acid (H2SO4) is commonly used to preserve acidity in a water sample for testing due to its strong acidic properties. By adding sulfuric acid, the pH of the water sample can be lowered, which helps in stabilizing certain analytes and preventing biological activity that could alter the chemical composition during the analysis. Maintaining a consistent pH is crucial for accurate results in various tests, such as those measuring metal ions or nutrients.

While hydrochloric acid can also adjust pH levels, sulfuric acid is often preferred in certain analytical methodologies due to its dual ability to act as both a strong acid and a dehydrating agent, enhancing the stability of specific water samples. Acetic acid and citric acid are weaker acids and may not effectively preserve the required low pH during the testing period or might not adequately stabilize all analytes required for analysis.