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<div class="moz-cite-prefix">Good afternoon Tonya,</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">interesting question - do you use pure
ethanol, or denatured ethanol, and if the latter, which denaturant
is added?</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">If you use the bubbler to aerate the
ethanol to fix it, my first thought would not be the oxygen
(assuming that you do not use pure, bottled oxygen for mixing),
but the carbon dioxide, which surely leads to an acidification of
the remaining water fraction, even more so, if distilled or
bi-distilled water is used to dilute the ethanol, because
distilled water has a very high affinity for carbon dioxide. Even
though a bicarbonate-puffer system establishes, the pH is rather
at the low end and usually around pH 4-5 in distilled water, so
rather acidic. This surely is different in tap-water (assuming it
is of certified quality without any additives such as chlorine),
especially if it is calcareous. But still, when mixing both
fluids, you shift the dissolving equilibrium, and what you can
spot is a lot of fine air bubbles that escape from the mixture
(carrying capacity for the physically dissolved gases shifted),
and (usually) a fine white precipitation (calcium carbonate).</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Thus the carbon dioxide likely has more
effect than the oxygen on the acidity of the aqueous fraction of
the mixture. <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Next step: secondary reactions like
oxidation. <br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">While ethanol is a rather stable
molecule, less stable molecules would be attacked and oxidised
first, because their unsaturated polar bindings have the higher
affinity to attract electrons. For example, residual formaldehyde
escaping from specimens might be oxidised to formic acid. Same
applies to highly polar denaturants like ketones, which are more
susceptible to be oxidised. The more such molecules are present
and oxidised, the less the ethanol will.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">And you less likely can prevent this by
mixing the ethanol with N2, because stirring the mixture will also
allow other gases to dissolve (unless this is done in a
hermetically closed atmosphere). And even if, upon initial filling
or topping, the fluid will have a lot of contact with the
surrounding air and will be stirred up, and carbon dioxide and
other gases will dissolve etc. ...</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">We you use a big stick to stir the
fluids when mixing the ethanol in a drum, we usually mix 60 litres
and let it rest for two days until we use it. We have two of these
drums, which is sufficiently enough for our daily work, and we are
careful when filling jars to avoid any air bubbles, i.e. we fill
in the ethanol slowly.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Hope this helps,</div>
<div class="moz-cite-prefix">Dirk<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Am 22.06.2021 um 05:12 schrieb Haff,
Tonya (NCMI, Crace):<br>
</div>
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<p class="MsoNormal">Hello all,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">We typically use a fish bubbler to mix ETOH
and water together when we mix up 70% ETOH. We are in the
stages of planning a new building, and I recently got the
below feedback about doing this – the dangerous goods
consultant says that this has the risk of acidifying the
solution, and that using N2 to mix the solution might be a
better idea. Do any of you have thoughts on this? If so, I
would really appreciate hearing them!<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Cheers,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Tonya<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b><span style="mso-fareast-language:EN-AU"
lang="EN-US">Email:<o:p></o:p></span></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As per our conversation last week, you
mentioned that CSIRO plan on using air to bubble through their
ethanol solutions to help mix the solution. Can you please
confirm if this is correct with CSIRO?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Normally when you mix/bubble air through
ethanol solutions, you may run the risk of oxidation of the
ethanol, although this reaction is very slow, you may generate
some acetylaldehyde and eventually ethanoic acid.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Can you confirm with CSIRO if using
nitrogen is better? This would still help mix the solutions
and would have the added benefit of degassing the ethanol by
removing dissolved oxygen from the solution. This long term,
would help minimise the risk of oxidation of the ethanol and
generation of acetylaldehyde and eventually ethanoic acid.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-AU"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-AU">Regards<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-AU">Paulo
Da Silva<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p>Dr Paulo Da Silva<br>
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