Chromatography Forum

Dear colleagues,

I’m experiencing problems with acetonitrile for the second time. I use acetonitrile and water in separate containers for my HPLC elutions.
After three weeks of use a triphasic mixture appears in my acetonitrile container. The acetonitrile becomes cloudy, there’s a denser liquid at the bottom of the container and crystals...
This mixture smells strongly ammonia and the denser solution is very basic (pH=14).
Some acetonitrile left in the original tank is still "normal".

I’ve read in the archive that acetonitrile could polymerise in the presence of an acid or a base.
My acetonitrile container is capped then nothing could fall in the bottle, and the technical support from Waters told me that nothing could flow back trough the channel.
Do you think it could come from the dishwasher? If the bottle is not well rinsed it could be some dishwasher detergent (which is alkaline) left inside.
Anyone has experienced this problem?
I would really appreciate some help on this.
Thanks a lot.

Erwan

We use ACN a lot, leave it in separate reservoirs on top of the HPLC units, and I've never seen this happen. Rinse your reservoir bottles with a HPLC water, then a little ACN before using if you suspect a contamination issue.

Thank you for your quick reply and your advices. I know that’s not usual at all and I’d like to understand how it happened.
It appears that crystals at the bottom of the container are soluble in water. And the pH of this solution is very basic and smells ammonia.
Is ACN able to react with detergent (quaternary ammonium..) or phosphates to produce ammonia?
Cheers.

Hi

Think a contamination of your bottle is the most likely cause, for example if someone left a bottle to dry without rinsing properly some ions and even pyridine can bind very hard to the surface, HCl is sometimes much easier to use to clean out such stuff.

If recalling right, so yeah possibly ACN can over time reversible can accept a proton from lets say ammonium ion so you get some amonia .
But as you said your self it is more likely that ACN undergo a basic addition reaction than a reduction to C2H6 + NH3 (unless you keep the enzyme nitrogenase in your bottles).

Hi Erwan,

Your challenge seems some contamination in your ACN bottle. I did never see it before. Did you try to change your ACN bottle by other clean bottle? I saw chromatographists using reusable bottles as HPLC solvent container without difficulties.

Have nice elutions!!

Carlos Teixeira

Hi

Thank you Krickos and Carlos. I always use containers which have been washed by the dishwasher. You’re right Krickos, next time I’ll try HCl to remove eventual residues.

Before any more adventurous nitrile chemistry is invented it might be worthwhile to look at

http://www.chemguide.co.uk/organicprops ... lysis.html
http://www.chemguide.co.uk/organicprops ... ction.html

Thank you! That's very interesting.