This comparator uses a simplified measurement method based on the unique reaction that occurs when a DPD reagent is added to water containing residual chlorine and the color of the water changes to light reddish purple depending on the amount of residual chlorine. You add the reagent once. (When measuring total residual chlorine, you add reagents twice as the optional potassium iodide is also used.)
This comparator can identify free residual chlorine and total residual chlorine.

Main Applications
・ To control residual chlorine in tap water for drinking, swimming pools for regular swimming or competitions
・ To control residual chlorine in public bathes or hot springs as a measure against legionnaires’ disease
・ To control total chlorine of water for dialysis

● DPD reagent is a powder reagent and is individually packed so one bag is used each time. Standard reagent package for 100 tests and economy pack for 500 tests are available.
● As DPD reagent contains a pH buffer, it adjusts the pH of sample water so that the color can be measured in a stable condition. (Measurements can be performed stably when the pH of sample water is between 3 and 10).
● When the optional potassium iodide reagent is also used, total residual chlorine can be measured. The combined residual chlorine concentration can be calculated from the difference between the total residual chlorine concentration and free residual chlorine.
● As the expiration date of the reagent is printed on the box, you can easily check if the reagents have expired.
● As the color comparison plate can be removed, the product can be managed easily and economically.

Measurement Method—For Residual Chlorine (Free Residual Chlorine)
・ Fill two rectangular test tubes with sample water until they are 80 % full and place them into the left and right test tube pockets on the main unit.
・ Pour 10 mL of sample water into the remaining rectangular test tube.
・ Add the DPD powder reagent and mix it.
・ Place the sample water in the center hole for color comparison measurement.

Measurement Method—For Combined Residual Chlorine
・ After measuring free residual chlorine, add one spoonful (0.1 to 0.5 g) of the separately available potassium iodide using the dispensing spoon provided, and dissolve it.
・ Leave the solution for approximately 2 minutes. Then, insert it into the center test tube pocket of the residual chlorine comparator, compare the color against the colors on the color comparison plate, and find the concentration of total residual chlorine from the applicable standard color.
・ Obtain the combined residual chlorine concentration using the calculation formula.
Combined residual chlorine (mg/L) = Total residual chlorine (mg/L) - Free residual chlorine (mg/L)