For testing residual chlorine, which method determines free available chlorine with minimal interference?

The DPD-colorimetric method is optimal for testing residual chlorine, particularly free available chlorine, due to its sensitivity and specificity. This method involves the use of DPD (N,N-diethyl-p-phenylenediamine), which reacts with free chlorine to produce a colored compound. The intensity of the color is directly proportional to the concentration of chlorine present and can be measured using a spectrophotometer.

One of the key advantages of the DPD-colorimetric method is its minimal interference from other substances that may be present in water samples. This makes it highly reliable for accurately measuring chlorine levels, which is crucial for ensuring safe water quality and compliance with health regulations.

The other methods may not offer the same level of specificity or could be more affected by the presence of other oxidants or substances in the water, which could lead to inaccuracies in measuring free available chlorine. Hence, the DPD-colorimetric method stands out as the preferred choice for its reliability and reduced interference in testing residual chlorine.