Cher Alain:
Here is what makes Helium the best option, followed by Argon, and why
Nitrogen is not recommended for blanketing of reagents in DNA
synthesizers:
The danger comes from the humidity, and the air could often be quite
humid, given the fact that water runs freely in the labs and all cities
are built next to a large river or sea. Atmospheric air consists of 80%
Nitrogen. The specific gravity of pure Nitrogen is 0.967 (specific
gravity is defined in relation to the 1.000 being the air at the same
conditions: 20 deg Celsius and normal 1 atm pressure at sea level).
Therefore, there is no need to extensively prove that Nitrogen will mix
very well with water vapors, and that atmospheric air will mix perfectly
well with the nitrogen from your bottle at all points of contact within
your lines. The humidity will easily sneak in from outside into your
lines.
Now, argon is better than nitrogen. Unfortunately, while the molecular
weight of Argon is 40 as opposed to 14 for Nitrogen, this does not
translate into large difference in specific gravity, because Nitrogen's
specific gravity is mere 1.376. Hence, Argon will quite easily mix with
air.
Finally, Helium is the best because it is quite different from nitrogen
and air, its specific gravity is only 0.138. Helium will stay on top,
will not mix well with humid air, will isolate the reagents, and will be
much better in keeping your lines dry.
When Beckman and PerSeptive introduced Helium, they got an upper hand
over the ABI in reagent life on the machine and in trityl readout data,
primarily because of Helium.
It is up to you to decide whether to use Nitrogen, Argon or Helium. For
me, this is a no-brainer: It you spend $300K per year on reagents, of
which at least $200K is AAA (amidites, activator, acetonitrile), and $3K
on Helium, it is not worth it to try to "save" $1.5K of those $3K, and
waste $50K of AAA (to say nothing of the technician time and reagent
cost for re-synthesis, the additional delays, and the hordes of lost
customers). The most common problems with DNA synthesis come from wet
amidites and blocked lines (often G-lines). If you substitute Nitrogen
for Helium, your G amidite bottle and the G line may soon be used to
demonstrate a crystallization experiment in progress, similar to what
happens when you pour water into that amidite solution.
Actually, if you move your lab from France a couple of hundred miles
south, into southern Algeria (in the Sahara desert), you may use a
compressed air (from a compressor) instead of bottles with pure gases,
because humidity there is what hot weather is here in Canada (the days
will soon start to get shorter, and I am still freezing in my winter
jacket). But again, while synthesizing DNA in Algeria may keep your DNA
reagents perfectly dry, you would risk having your own DNA decomposed by
the fundamentalists...
Best regards,
victor
____________________
Alain Laurent a Ècrit
Dear All
As anybody ever try to use anydrous nitogen instead of anydrous helium
or Argon on the Expedite synthesiseurs ?
Why should not it work ? I personnaly use now argon instead of helium
(wich is double the price !) . So I was wondering if Nitrogern could do
the job ! ?
Best regards
Thank You
Alain
**************************************
Alain LAURENT Ph. D
DNA&Peptide Chemistry
ESGS Groupe CYBERGENE
11, rue Claude Bernard
35 400 Saint MAL0
FRANCE
Tel: +33 (0)2 99 21 90 40
Fax: +33 (0)2 99 21 90 41
e-mail: a.laurent@eurosequence.com
http://www.eurosequence.com
**************************************
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