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Chlorine Testing in Pools and Spas using DPD

Disinfection using DPD

Chlorine is used as a primary disinfectant because of its effectiveness in killing potentially harmful organisms. It forms hypochlorous acid in pool water whose effectiveness at disinfecting is influenced by the other chemicals that are in the pool – primarily pH and the amount of waste present.

  • Hypochlorous acid that has not reacted with bather waste is “free chlorine” and must be carefully monitored in order to guarantee a safe pool.
  • Hypochlorous acid that reacts with bather waste forms “combined chlorine” which reduces its power to disinfect and is also associated with the unpleasant smell and irritation of eyes and nose that can occur in pools. ‘Combined chlorine’ results from the reaction between ammonia-based compounds from bather waste and chlorine to form monochloramine, then dichloramine.

The Palintest DPD Method

The DPD indicator, an abbreviation of diethyl-p-phenylene diamine, is available under different forms: powder, liquid and tablets. Dr Palin spent the initial part of his career at Palintest developing the DPD system, firstly as a liquid and then as convenient tablets numbered 1 to 4. Tablets are easier and safer to handle for convenient dosing and optimum storage.

All forms of DPD react with pool water containing chlorine, bromine or ozone, coloring the water sample in various shades of pink: the deeper the colour, the higher the concentration of sanitiser. The DPD method is based on measuring the intensity of colours produced by the reaction between reagents in the DPD tablets with the sanitisers to be measured in the water. Visual colorimetric techniques will help to translate the intensity of colors into values using calibrated colour charts. However, photometers can digitally analyse the colour generating results with more accuracy by referring to calibration data stored in the instrument memory.

A range of Palintest DPD tablets can be found on our website along with Photometers and accessories to measure Chlorine in pools.

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