[enahs]

OK, solid Ammonium Acetate can be decomposed to acetamide with heat. What about in aqueous solution, over time with gentle heat?

I hate organic chemistry.

[AWK]

Write down a reaction. What will happen when you add water to this equilibrium reaction?

[enahs]

Yes I know it is a product and will shift it more towards the reactants.


The reason I ask is, one of our HPLC solvents is an Ammonium Acetate buffer. And we were getting odd results. Now, the HPLC is right next to the window, and the bottle of solvent basically sits on the window sill. I am not sure how hot it gets there, but I know the temperature rises substantially.

After I made a fresh solvent batch yesterday, the oddness seemed to go away. So I am trying to figure out if it was just a bad batch, or something like that conversion is happening. As it had been sitting in the window sill essentially for ~2 weeks. And does get full sun (but the windows block UV).


I just do not know if this reaction even happens in aqueous solution, as the salt is now dissociated.

And yes I know it is bad to store the solvents in the window sill. I did not put the HPLC system there...

[Arkcon]

A number of things can happen to HPLC eluents over time.  Evaporation, loss of volitile components, even microbial attack, all over time frames and under conditions where you wouldn't expect it.

Trying to pin down what's happening and why can be problematical, and time consuming.  Probably the most practical solution is to prep the eluent fresh, as needed for a batch of analytical runs.

[enahs]

Yep Arkcon, with regards to what can happen.


No to a fresh batch every time. This can lead to changes and inconsistency in the solvent. When you want to compare two trails, if the solvent was a different batch, you have to ask "was the solvent pH or concentration different from the previous trial, or did something different happen this time?".

It is a balance between the two. The things you listed will not be a concern for us over a weeks time; I just had the idea while driving home about it possibly being converted to acetamide via heat. But now that I think about it when I am not driving home, it is of no concern.

[Arkcon]

I worked at one pharma company that maintained policy of the value of keeping batches consistent.  I would prep 4 L of a 0.1 M triethylamine  acetate eluent, and store half in the fridge.  I gave it a (somewhat arbitrary) usage date of one month.  Even so, as time passed, this one batch changed it's baseline over the space of one month, even when stored refrigerated.

I worked for another pharma company that always prepared fresh eluent, according to method, for each run.  No eluent older than 24 hrs (even 60:40 methanol:water) was allowed.

My point is that you can justify either point of view, as a company policy, and still be within FDA regulatory compliance.  So perhaps it's worth revisiting your policies for just this eluent system, or just this analysis, or just this sunshiny system.