Question
Asked 25th Apr, 2018

How to keep the pH of Deionized water 7?

I prepared deionized water through deionizer, but unfortunately the pH dropped to 5. Now how can i resume the pH to 7, to use this water in PCR and other solutions preparation?

Most recent answer

25th Nov, 2019
Mohammad Khani
Isfahan University of Technology
you should keep this water in an isolated container and you should not allow this container to be exposed with air in a direct contact manner

Popular Answers (1)

26th Apr, 2018
Emmanuel Ifeanyi Obeagu
Michael Okpara University of Agriculture, Umudike
Dear Hashim, I understand your plight. In theory, the lack of ions means that deionized water should have a pH of 7. However, when deionized water comes into contact with atmospheric carbon dioxide, its absorption of the gas produces carbonic acid, which can reduce the water's pH to as little as 5.5. For this reason, the pH reading of deionized water is usually below 7. When measuring pH of D.I. water, the initial reading should be 7. If it is not, then the measuring instrument is not properly functioning. Some pH meters will not work because they need ions to give an accurate reading. A 7 is the reading before carbon dioxide has its effect. In order to keep the reading at 7 and avoid the problem of carbon dioxide lowering the reading, it is necessary to either keep the D.I. water from being exposed to air or boil the water to remove the carbon dioxide. The correct pH measurement is 7 for D.I. water, and the effect of carbon dioxide should be ignored.
7 Recommendations

All Answers (6)

26th Apr, 2018
Emmanuel Ifeanyi Obeagu
Michael Okpara University of Agriculture, Umudike
Dear Hashim, I understand your plight. In theory, the lack of ions means that deionized water should have a pH of 7. However, when deionized water comes into contact with atmospheric carbon dioxide, its absorption of the gas produces carbonic acid, which can reduce the water's pH to as little as 5.5. For this reason, the pH reading of deionized water is usually below 7. When measuring pH of D.I. water, the initial reading should be 7. If it is not, then the measuring instrument is not properly functioning. Some pH meters will not work because they need ions to give an accurate reading. A 7 is the reading before carbon dioxide has its effect. In order to keep the reading at 7 and avoid the problem of carbon dioxide lowering the reading, it is necessary to either keep the D.I. water from being exposed to air or boil the water to remove the carbon dioxide. The correct pH measurement is 7 for D.I. water, and the effect of carbon dioxide should be ignored.
7 Recommendations
26th Apr, 2018
Yuri Mirgorod
Southwest State University (Russia)
To maintain pH = 7 A bottle with deionized water is closed with a special tube with an expansion that is filled with CaO. CaO reacts with CO2 of air and it does not dissolve in water with the formation of carbonic acid.
3 Recommendations
26th Apr, 2018
Gyorgy Banhegyi
Medicontur Medical Engineering Ltd.
As explained by Dr Mirgorod, it is due to CO2 absorption, so it is unavoidable unless you prevent CO2 absorption. Yo may also boil the water time to time to remove dissolved gases.
1 Recommendation
29th Apr, 2018
Muhammad Hashim
Quaid-i-Azam University
Thank you so much for your valuable answers. Actually i want to use this deionized water for DNA extraction purposes like in solutions etc, i don't know what is the reason but the pH of my deionized water is below 5.5 which is acidic i am worrying about my DNA to be degraded by this acidic water, may be this is due to my deionizer, or any other technical problem.
kindly suggest me can i use these water for DNA extraction, Purification, Storage and PCR etc? if pH is less than 5.5?
13th Aug, 2018
Raymond Zhang
University of North Carolina at Chapel Hill
Hi Muhammad Hashim did you end up figuring out how to pH adjust the water for DNA extraction?
Can you help by adding an answer?

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