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Pool operators need to be confident that the sanitizer concentration is correctly dosed and controlled, for the health and comfort of bathers. Disinfection of swimming pools is usually achieved using chlorine and adequate free chlorine is needed to prevent infections, while eye irritation is minimized by keeping the combined chlorine residual as low as possible. The well-established DPD method, developed by Dr A.T. Palin (originally called the Palin System) is the test procedure of choice for free, total and combined chlorine, but also bromine and ozone due to its consistency and reliability. |
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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 shadesof pink: the deeper the colour, the higher the concentration of sanitizer. The DPD method is based on measuring the intensity of colours produced by the reaction between reagents in the DPD tablets with the sanitizers 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 analyze the colour generating results with more accuracy by referring to calibration data stored in the instrument memory. |
The principal tablets of the Palin System are numbered 1 to 4 as follows in Table 1:
|
Tablet |
Contents |
Parameter to measure |
|
DPD 1 |
DPD indicator plus buffer |
Free Available Chlorine |
|
DPD 2 (use with DPD 1) |
Stabilized KI for monochloramine activation |
CombinedChlorine |
|
DPD 3 (use with DPD 1) |
Stabilized KI for dichloroamine |
Total Chlorine |
|
DPD 4 |
All reagents in a single tablet |
Total Available Chlorine |
Additional tablets used in supplementary procedures are given below:
DPD tablets given in Table 1 can also be used when measuring alternative disinfectants such as bromine or ozone.
DPD methods to measure the different relevant sanitizers in the pool water with the Palintest range of products are summarized in Table 2.
|
Chemical |
Parameter tested * |
TabletsDPD required |
Comments |
|
Chlorine |
FreeChlorine |
1 |
Resultinmg/l Chlorine |
|
Total Available Chlorine |
4 |
Resultinmg/l Chlorine , Or 1 + 3 together |
|
|
FreeChlorine only |
1 |
A Result in mg/l Chlorine |
|
|
Total Available Chlorine |
3 |
B Result in mg/l Chlorine |
|
|
Combined Chlorine only |
Combined Chlorine mg/l Chlorine = B - A |
||
|
FreeChlorine only |
1 |
A Result in mg/l Chlorine |
|
|
Monochloramine only |
2 |
Monochloramine = B Result in mg/l Chlorine with DPD 2 - A |
|
|
Dichloramine only |
3 |
Dichloramine = C Result in mg/l Chlorine with DPD 3 - B |
|
|
Bromine |
Bromine PLUS Bromamine |
1 |
No need to differentiate between both, as both have disinfectant properties |
|
Bromineand Chlorine |
Bromine only Bromine PLUS Free Chlorine Bromine PLUS Total Available Chlorine Total Available Chlorine Combined Chlorine only |
Glycine*+1 1 + 3 (need 1) |
A Result in mg/l Bromine B Result in mg/l Bromine, Free Chlorine mg/l = 0.44 * (B - A) C Result in mg/l Bromine Total Chlorine mg/l Chlorine = 0.44 * (C-A) Combined Chlorine mg/l Chlorine = 0.44 * (C - B) |
|
Ozone |
Ozone only |
4 |
Resultmg/lOzone |
|
Ozone and Chlorine |
Ozone PLUS Total Chlorine Ozone only Total Chlorine |
4 Glycine*+ 4 |
A Result mg/l Ozone B Result mg/l Ozone Total Chlorine mg/l Chlorine = A - B |
* The glycine neutralizes chlorine.
The Palins DPD System ensures effective sanitation and guarantees a positive experience for the bather. More information to measure each parameter can be found in the instructions of our products, but do not hesitate to contact info@redstarvietnam.com you have any questions or require more information.
