Which of the following is a common preservative used in water sampling?

Sulfuric acid is indeed a commonly used preservative in water sampling, especially for preserving samples intended for analyzing certain water quality parameters. Its primary role is to lower the pH of the water sample, which can help stabilize certain analytes, particularly metals, by preventing the precipitation or alteration of these substances before analysis. Lowering the pH can also inhibit the growth of microbial organisms that could otherwise alter the composition of the sample.

In water quality testing, maintaining the integrity of a sample is crucial, and sulfuric acid is effective in ensuring that the sample reflects the true conditions of the water source at the time of collection. This preservation technique is particularly relevant in samples that are to be analyzed for nutrients, bacteria, or other parameters sensitive to changes in water chemistry over time.