What substance is used to preserve heavy metal samples?

The preservation of heavy metal samples is crucial for accurate testing and analysis in environmental compliance. Nitric acid is the preferred choice because it serves several essential functions in the sampling process. Firstly, nitric acid is effective at dissolving many heavy metals, which allows for a more stable sample that can be accurately analyzed. It also helps to prevent the adsorption of metals onto container surfaces, reducing the potential for contamination or loss of the analyte.

Moreover, nitric acid provides a low pH environment, which minimizes the risk of precipitation and ensures that heavy metals, particularly cationic species, remain in solution. This stability is critical for maintaining the integrity of the sample from the time of collection until analysis.

The other substances listed, while they may have their uses in different contexts, do not provide the same level of effectiveness in preserving heavy metal samples. For instance, sulfuric acid might create issues with certain metal species and can lead to precipitation. Hydrochloric acid, although it is useful for certain analyses, does not stabilize heavy metals in the same way as nitric acid. Acetic acid is primarily a weaker organic acid not suited for heavy metal preservation due to its higher pH and reduced capability to maintain metals in solution.

Thus, the choice of nitric acid as