What pH level should samples collected for cyanide analysis be adjusted to for preservation?

For effective preservation of samples collected for cyanide analysis, it is essential to adjust the pH level to greater than 12. This high pH is necessary because cyanide can exist in different forms depending on the pH level of the water. At elevated pH levels, cyanide is more stable and less likely to degrade over time, ensuring accurate analysis results.

When the pH is below 12, cyanide can convert to other forms or may evaporate, leading to potential loss or transformation of the pollutant being measured. By maintaining a pH greater than 12, any free cyanide remains in its most stable and detectable form, allowing for a more reliable assessment of its concentration in the sample. This procedure is a standard practice in wastewater testing to ensure the integrity of the sample prior to analysis.

In contrast, other pH ranges mentioned do not provide the necessary stability for cyanide, leading to complications in accurate measurements during analysis.