Which chemical is used for measuring residual chlorine?

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Multiple Choice

Which chemical is used for measuring residual chlorine?

Measuring residual chlorine uses a colorimetric reagent that reacts specifically with chlorine to produce a visible color. The DPD reagent (N,N-diethyl-p-phenylenediamine) is oxidized by chlorine to form a pink to red color, and the intensity of that color corresponds to the chlorine concentration. This method is standard because it provides a direct, sensitive readout that can be matched to a color chart or measured with a photometer, and it can be used to determine both free and total chlorine depending on the testing steps. Phenol red and methyl orange are pH indicators, not chlorine reagents, so they don’t quantify chlorine residual. EBT is a dye used in some chlorine tests but is not the universally adopted reagent for measuring residual chlorine in typical WTPO practice. Therefore, the chemical used for measuring residual chlorine is DPD.

Measuring residual chlorine uses a colorimetric reagent that reacts specifically with chlorine to produce a visible color. The DPD reagent (N,N-diethyl-p-phenylenediamine) is oxidized by chlorine to form a pink to red color, and the intensity of that color corresponds to the chlorine concentration. This method is standard because it provides a direct, sensitive readout that can be matched to a color chart or measured with a photometer, and it can be used to determine both free and total chlorine depending on the testing steps.

Phenol red and methyl orange are pH indicators, not chlorine reagents, so they don’t quantify chlorine residual. EBT is a dye used in some chlorine tests but is not the universally adopted reagent for measuring residual chlorine in typical WTPO practice. Therefore, the chemical used for measuring residual chlorine is DPD.

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