[Nhcoll-l] FW: use of air to bubble through ethanol to mix solutions.

Tue Jun 22 21:22:43 EDT 2021

Dear all,

Thank you so much for your replies, I very much appreciate it. Sounds like the consensus is mix with a paddle or stirring rod and don't worry about using a bubbler with either air or N2, and let the mixture stand for 2 days. I thought I had read that 24 hours was sufficient? At any rate, two days is ok if we decant into larger containers (right now I decant into 20L containers, which can empty fairly quickly!). I use good quality tap water, not deionised water, to avoid increased acidification.

I wish that we could use glass with ground glass tops for everything, but unfortunately that's not an option for us. In fact in Australia any quality glass jars at all are a challenge at the moment. At least all of our smaller specimens (2L jars and under) are in glass, but it does makes me worry a little bit about our larger specimen, which are in HDPE drums. It's a challenge to get fluid preservation perfect!

Thanks so much for your feedback!

Tonya

From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu> On Behalf Of A.J.van_Dam at lumc.nl
Sent: Tuesday, 22 June 2021 7:03 PM
To: neumann at snsb.de; nhcoll-l at mailman.yale.edu
Subject: Re: [Nhcoll-l] FW: use of air to bubble through ethanol to mix solutions.

Dear Tonya,

When a fluid like ethanol is stored in containers (partly) made of breathable materials (such as PE and PP) the fluid will take up an amount of CO2 and O2 from the surrounding atmosphere until the solubility equilibrium has been reached. These gasses will be used up by the degradation reactions (e.g. acidification) that take place inside the specimen jar creating new demand to maintain the solubility equilibrium. The best way of slowing down the inevitable acidification of your fluid is creating a barrier for these gasses to enter the jar by using low-permeable container materials for these gasses. Glass jars with glass lids and a low oxygen permeable sealant are still the best way to severely slow down these degradation processes.

To my opinion, flushing ethanol with nitrogen does not have much effect on preventing acidification in the long-term when subsequently this mix is poured into containers that are not air-tight or are made of materials that are highly permeable for air.

Kind regards,

Dries
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From: Nhcoll-l <nhcoll-l-bounces at mailman.yale.edu<mailto:nhcoll-l-bounces at mailman.yale.edu>> On Behalf Of Dirk Neumann
Sent: dinsdag 22 juni 2021 9:12
To: nhcoll-l at mailman.yale.edu<mailto:nhcoll-l at mailman.yale.edu>
Subject: Re: [Nhcoll-l] FW: use of air to bubble through ethanol to mix solutions.

Good afternoon Tonya,

interesting question - do you use pure ethanol, or denatured ethanol, and if the latter, which denaturant is added?

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).

Thus the carbon dioxide likely has more effect than the oxygen on the acidity of the aqueous fraction of the mixture.

Next step: secondary reactions like oxidation.

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.

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. ...

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.

Hope this helps,
Dirk

Am 22.06.2021 um 05:12 schrieb Haff, Tonya (NCMI, Crace):
Hello all,

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!

Cheers,

Tonya

Email:

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?

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.

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.

Regards
Paulo Da Silva

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