DPD Tablets measure Chlorine levels, the most common form of disinfectant in water. They are widely used in swimming pools, drinking water and industrial process water.
How do DPD Tablets Work?
When using Chlorine to disinfect water, the aim is to kill off the bacteria (pathogens) and then to leave a small amount of active (free) Chlorine in the water. This remaining Chlorine is also known as the “residual Chlorine” and is important as it is available to disinfect further contamination of the water.
Combined (total) Chlorine is the sum of the free Chlorine available in the water to disinfect future germs and the Chlorine that has already been already used and bound together with pathogenic molecules.
It is vital to calculate the correct amount of Chlorine to be added – too much is negative to health and wastes money, too little can result in a high level of disease causing pathogens.
The Chlorine demand can be determined by deducting the residual chlorine from the total amount of Chlorine added. It can change with time, pH and the amount of impurities in the water.
Measuring High Chlorine Levels
DPD tablets can accurately measure Chlorine levels from 0.001 mg / l to 10 mg /l . When a sample has a chlorine level that is higher than 10, the colour is bleached out of the Chlorine tablet – there is a quick show of pink colour and then the sample returns to its original colour. Dilutions can be done to determine high range Chlorine levels.
Quality of DPD Reagents
- DPD reagents are produced on the basis of international standard methods and the ISO standard method
- The chemicals are of a crystalline white nature. If a reagent (tablets or powder) is not white but has turned grey/brownish or purple in colour, it has deteriorated. The use of deteriorated products must be avoided as they will give false results
- DPD is most commonly used in tablet form, but is also available in powder and liquid form – which should you choose?
Chemical reagents, eg. DPD tablets are used with a comparator or a photometer to produce a measurable scientific result.
Should you use a comparator or a photometer?
Updated September 2019.
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