What reagent is typically added to bottles for total coliform samples?

Total coliform samples are typically collected to assess the microbiological quality of water. When these samples are taken, it’s crucial to preserve them to prevent any changes in the microbial populations before analysis. Sodium thiosulfate is specifically used as a dechlorinating agent. In many water systems, chlorine is employed for disinfection, and residual chlorine can adversely affect the viability of the coliform bacteria during sample storage and transport. By adding sodium thiosulfate, chlorine is neutralized, which helps to maintain the integrity of the sample for accurate microbiological testing.

The other reagents listed have different primary functions and do not serve the same purpose in preserving total coliform samples. Sodium chloride is often used as a precursor in certain biochemical processes, while sodium bicarbonate is primarily used to buffer pH levels. Potassium hydroxide is a strong base often involved in various chemical reactions but is not used for preserving microbial samples. Therefore, sodium thiosulfate stands out as the necessary reagent for ensuring accurate total coliform sample analysis.