Which method is commonly used to conduct chlorine residual testing?

The DPD method, which stands for N,N-diethyl-p-phenylenediamine, is a widely recognized colorimetric technique used for testing chlorine residuals in water samples. This method involves adding a DPD reagent to the water sample, which reacts with free chlorine to produce a pink color. The intensity of the color is proportional to the concentration of chlorine present in the sample. This color can be measured using a spectrophotometer, allowing for accurate quantification of chlorine levels.

The popularity of the DPD method in water quality testing stems from its sensitivity and ability to provide rapid results. It is particularly favored for its straightforward procedure, giving results in a relatively short amount of time, which is critical for operational water quality monitoring.

Other methods listed, such as Fenton's reagent and titration using iodine, are not commonly employed for routine chlorine residual testing in water. Fenton's reagent is more associated with oxidation processes in water treatment, while iodine titration is typically used for different types of analyses. Gas chromatography is a sophisticated technique that is not suited for measuring chlorine residuals directly, as it is primarily utilized for the analysis of volatile and semi-volatile organic compounds.