Why must chlorine residual samples be analyzed immediately?

Chlorine residual samples must be analyzed immediately primarily to avoid dissipation. Chlorine is a highly reactive substance that can rapidly break down in the presence of organic matter, heat, and light. If the samples are not analyzed quickly, the concentration of chlorine can decrease, leading to inaccurate results. This dissipation can occur in a matter of minutes, making it crucial to carry out the analysis as soon as possible to obtain a reliable measurement of the chlorine residual present in the sample.

While contamination, preservation of color, and consistency of results are important considerations in lab analysis, they are secondary to the immediate analysis of chlorine residuals because the primary concern is maintaining the integrity of the chlorine concentration in the sample. If the chlorine concentration decreases due to dissipation, it fundamentally alters the data, regardless of other factors. Therefore, timely analysis is essential to ensure that the chlorine levels reflect the actual conditions in the wastewater treatment process.