Which reagent is commonly used for field testing chlorine residual?

The reagent commonly used for field testing chlorine residual is DPD (N,N-diethyl-p-phenylenediamine). DPD is a colorimetric reagent that reacts with free chlorine in the water, producing a measurable color change proportional to the concentration of chlorine present. This makes it a reliable method for determining chlorine levels in water supplies quickly and accurately.

The DPD method is widely accepted and utilized in water quality testing because of its sensitivity and relatively quick results, making it ideal for water operators in the field who need to monitor disinfectant levels to ensure safe drinking water. Other reagents mentioned, such as nitrite and phenol red, serve different purposes and are not designed for measuring chlorine residuals. Universal indicators, while useful for determining pH levels, are not specific to chlorine testing. Therefore, DPD stands out as the appropriate choice for this particular application.