RE: [Histonet] Dionized vs distilled water

From:"Smith, Allen"

Tap water varies a little from one water system to another.  It is usually a very dilute solution of the carbonates and chlorides of calcium, sodium, and copper.  Its pH is usually a little over 7, so it acts as a very weak base.  (Mine is 7.4)  It must be used when the  protocol calls for it. 
Distilled and deionized water contain so few ions that neither one will act as a weak base.  For most purposes, distilled and deionized water are interchangeable.  It is easier to contaminate a deionizing system, but one can contaminate a distilled water system.  Small, lab-sized systems are less likely to become contaminated with bacteria or minerals than large building-sized systems are. 
If you need really pure water, boil 600 ml of deionized water and add 6 mg of potassium permanganate to it and distill the water.  Discard the first 100 ml of distillate.  The next 300 ml will be very pure water, but I can think of no biological use for it.  (Such very pure water is sometimes used for physics experiments.)
Both distilled and deionized water pick up carbon dioxide on standing and become weak solutions of carbonic acid.  If you work alone, its pH will probably be 6.9; if there are several people in the lab, the pH may fall to 6.8.
-----Original Message-----
From: Morken, Tim - Labvision []
Sent: Tuesday, October 28, 2003 12:53 PM
To: '';
Subject: RE: [Histonet] Dionized vs distilled water

Distilled water is classically produced by heating water to evaporation and subsequent condensing on a cold surface. In the process most impurities are either evaporated off ahead of the water (in the case of most organics), or left behind (in the case of minerals). The water is also effectively deionized because the salts are left behind. It is fairly pure water. To get very pure water it needs to be re-distilled several times.


Deionized water is classically passed through a salt bed or ionized resin bed that captures the mineral ions (ie, a "water softener"). The water is not necessarily pure, however, especially in regards to organic chemicals. Reverse osmosis is also used now days to deionize water.



High quality water systems these days are some combination of filters, distillation, deionizing resins and reverse osmosis.


Tim Morken


-----Original Message-----
From: []
Tuesday, October 28, 2003 7:45 AM
Subject: [Histonet] (no subject)


while studying for my exam on the different fixatives and there ingredients....i have noticed that some call for distilled water and some use the term deionized water.  Is there a difference?

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