Which color does the DPD test indicate when chlorine is present?

Which color does the DPD test indicate when chlorine is present?

• A. Blue
• B. Yellow
• C. Pink to Red
• D. Green

Answer: (C)

The test works by using a DPD reagent that reacts with chlorine to produce a colored dye. When chlorine is present, the reaction turns the sample pink to red, and the depth of the color grows with higher chlorine levels. That pink-to-red indicator is what you read against a color chart to estimate the chlorine concentration in parts per million. If there’s little or no chlorine, the color stays colorless or only a pale pink, but any noticeable chlorine shows up as pink to red. Colors like blue, yellow, or green don’t result from this DPD reaction with chlorine, so pink to red is the telltale sign of chlorine presence.

The test works by using a DPD reagent that reacts with chlorine to produce a colored dye. When chlorine is present, the reaction turns the sample pink to red, and the depth of the color grows with higher chlorine levels. That pink-to-red indicator is what you read against a color chart to estimate the chlorine concentration in parts per million. If there’s little or no chlorine, the color stays colorless or only a pale pink, but any noticeable chlorine shows up as pink to red. Colors like blue, yellow, or green don’t result from this DPD reaction with chlorine, so pink to red is the telltale sign of chlorine presence.