Which three laboratory methods are approved to detect total chlorine residuals according to TN regulations?

The approved laboratory methods to detect total chlorine residuals focus on accurate and reliable measurement techniques that adhere to state regulations. Among these, the DPD (N,N-diethyl-p-phenylenediamine) colorimetric method stands out as a widely used technique for measuring chlorine levels in water. It is particularly favored for its ease of use, rapid results, and sensitivity to different chlorine species.

The option mentioning DPD color metric correctly identifies this recognized method. Additionally, the inclusion of metric back titration speaks to the traditional analytical chemistry techniques that can also provide accurate chlorine residual measurements under specific conditions.

Understanding the characteristics of these methods emphasizes the importance of using scientifically validated procedures for water quality monitoring, especially regarding harmful substances like chlorine.

The other methods listed in the other options do not align with prevalent practices for measuring total chlorine residuals. For instance, ion chromatography is primarily used for different applications such as anions and cations analysis and does not typically focus on total chlorine measurement. Specific ion electrodes, while useful, usually target specific ions and may not effectively measure overall chlorine residuals.

Thus, the accurate combination of methods in the correct choice allows for precise monitoring of chlorine in wastewater, ensuring compliance with regulatory standards.