Which acid is used to acidify dissolved ion samples to pH less than two?

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Multiple Choice

Which acid is used to acidify dissolved ion samples to pH less than two?

Explanation:
Acidifying dissolved ion samples to pH below 2 is a preservation step in water surveillance that keeps metals in solution and slows down biological activity. A strong mineral acid is needed, and nitric acid is the most suitable choice because it fully dissociates to create a stable, highly acidic medium and is broadly compatible with common analytical techniques like ICP-MS and AAS. It minimizes interference from added anions; unlike hydrochloric acid, it avoids chloride complexes that can complicate metal measurements, and unlike sulfuric acid, it doesn’t risk forming insoluble sulfates for many metals. Acetic acid, being a weak acid, cannot reliably push the pH down to below 2. So, nitric acid is used to achieve the desired acidity.

Acidifying dissolved ion samples to pH below 2 is a preservation step in water surveillance that keeps metals in solution and slows down biological activity. A strong mineral acid is needed, and nitric acid is the most suitable choice because it fully dissociates to create a stable, highly acidic medium and is broadly compatible with common analytical techniques like ICP-MS and AAS. It minimizes interference from added anions; unlike hydrochloric acid, it avoids chloride complexes that can complicate metal measurements, and unlike sulfuric acid, it doesn’t risk forming insoluble sulfates for many metals. Acetic acid, being a weak acid, cannot reliably push the pH down to below 2. So, nitric acid is used to achieve the desired acidity.

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