summary of question related with distilled water

Thu Jul 1 20:45:45 EST 1993


    A couple of weeks ago, I asked a question about the pH
of 'distilled' (and not 'destilled') water and its effects in
the preparation of a buffer to calibrate a pH-meter.
    I would like to thank everyone who took sometime to give
me a clue in the subject.  Below there is a summary of, in
my opinion, the most relevant and useful of the answers
(this doesn't mean that the others are not).

* For the calibration of pH-meters it is prefered commonly
available calibration buffers. This is more precise than
self-made solutions.  (sensen at

* Dissolved carbon dioxide in the water results in HCO3- and
thus a drop in pH to around 6.0 - 6.5, even in 1-day-old
distilled water. (Steven K Harrison
<sharriso at>).  By boiling the
distilled water the CO2 is removed. (Thorben Lundsgaard
<KVLXTL at>)

* any salts or acids you mix in to make a buffer will
completely mask the CO2 effects. (psconk at
(Paul Conklin)

* the apparent acidity of your water should not make any
appreciable difference for what you wish to do because your
buffer salts will be present in many orders of magnitude
greater concentration than the apparent H+ concentration
differences that are making your water not neutral pH. Error
in weighing out the buffer salts is much more likely to
introduce error, in my opinion. (hernlem at
(Brad Hernlem)

    For those of us, who are working with plant 'tissue'
('in vitro', according to Pierik) culture, also raised some
interesting points, specially the last two.

* Something else worth mentioning, if you are preparing
plant tissue media like Murashige-Skoog medium, you should
be aware of two things.
* 1. The medium is very poorly buffered and will change pH
dramatically when plant cells or tissue are growing in it. I
have experienced that suspension cultured carrot cells will
take MS medium down as low as 3.8 pH without pH control.
(The direction of pH shift will depend upon whether the
cells are using ammonia or nitrate. Generally, ammonia is
utilized first and so the pH drops)
* 2. The medium will change pH dramatically upon autoclaving
and will also shift over time. This appears to be caused by
precipitation of iron from the medium.
If you must autoclave your medium, try out several initial
pHs and find the one which yields your desired pH after
autoclaving. Even if you filter sterilize your medium, the
pH will change with time but much more slowly.
(hernlem at (Brad Hernlem))

* Beware of storing water in plastic carboys if you are
using it for plant tissue culture.  Polypropylene is OK, but
regular plastic carboys have plasticisers (pthallates) that
are potent inhibitors of photosynthesis.
(cdelwich at (charles francis delwiche)

* Don't forget that water distilled in _glass_ contains
traces of silicates and borates leached from the glass.
It's high enough to be considered a problem in micronutrient
experiments. (ajt at (Tony Travis)

     Concerning the precipitation of ion by autoclaving.
Does anybody know if this happens also when chelated (EDTA)
iron is added?



  Victor M. Jimenez            vjimenez at
       CIGRAS                  Tel. (506)-24-8554
Universidad de Costa Rica      Fax. (506)-53-3762
 San Jose, Costa Rica

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