What is the relationship between the intensity of color change in DPD method and chlorine concentration?

The DPD (N,N-diethyl-p-phenylenediamine) method is a widely used technique for measuring free chlorine concentration in water. This colorimetric method relies on a chemical reaction where DPD reacts with chlorine, resulting in a color change. The intensity of this color change is directly related to the amount of chlorine present in the sample.

As the concentration of chlorine increases, more DPD reacts, leading to a more intense color development. Therefore, the intensity of color serves as an indicator of chlorine concentration. In practical applications, this allows operators to visually or instrumentally determine the concentration of chlorine simply by comparing the color intensity against a standard color chart or using a photometer for more precise measurements.

The other options do not accurately reflect the principles of the DPD method. An inverse relationship or claiming no relationship are inconsistent with established chemical principles underlying the DPD reaction. Additionally, while pH can influence other aspects of water chemistry, it does not have a direct impact on the interpretation of color intensity in the DPD chlorine measurement specifically.