Chromatography Forum

Sorry bothering you with this question:
Since some weeks we see a continuous decrease in our sensitivity. The instrument tuning and calibration is fine.
Now we have the impression that the formic acid might be the problem.

How stable is Formic Acid in the stock bottle, when it has been opened for use?

Thanks.

Formic acid is not particularly stable, it is easily oxidized. I would store any stock solutions in a refrigerator.

I have been using formic acid/ammonium format buffer a lot during the last year for LCMS analyses. We just store our formic acid under the hood. Formic is really stable as far as I can determine.

See MSDS sheet at

http://www.jtbaker.com/msds/englishhtml/f5956.htm

I had some trouble with ammonium acetate and ammonium format being decomposed by bacteria when stored at the mmolar level for many days. A sludge was formed and it stopped up all our frits. It was a mess to clear the system. Since then, we have always added 30 ml of either methanol, acetonitrile, or a mix of the solvents to 1000 ml of water when preparing buffered solution. This seems to reduce the rate of sludge formation so that we use the buffer for 5-10 days with no problems.

Washing our system with pure methanol seemed to clear our system of bacteria/sludge and washed stainless steel solvent reservoir frits with some aqueous nitric acid.

Ok, the particular bottle is open now for about one year and we store it under the hood.
What I find out in the literature so far is, that indeed its easily oxidized, may be by the oxygen of air.
Anyway, we will order a new bottle and will compare it with the old one.
Iterestingly, Baker writes, it is stable,
Merck (VWR) writes it is not stable, but does not metion a shelf life,
Sigma as well says, it is not stable, and mention a shelf life (I dont now how long they give it)

May be the oxidation produkts interfere with the ionization in ESI ??

Ours has been stored for many years, think it is OK.

Could get your sample titrated if you have the service within your organization.

Found this article on the specifics of oxidation..

http://www.chemistryquestion.com/Englis ... cacid.html

guess its correct..

on a safety related note, formic acid decomposes at room temperature over time to carbon monoxide, and if a ventilated cap is not fitted to the bottle, over-pressurisation can occur and explosion may result.

How do i now this.....experience!!

for more, refer to http://www.safety.uwa.edu.au/hazard_ale ... _explosion


Regards
Greg

That exploding formic must have been down under too long!

Seriously: In over 40 years of occasional use of formic acid I have never seen it in a vessel with a vented cap, nor have any exploded (I am now sitting 4 yards from two bottles, one ~ 10 years old, just opened that, not even a whizz). Checked a little into this: Con. H2SO4 liberates (dehydration) CO from formic, heat does also (but note its bp!). At room temp. the equilibrium between those species appears far on the formic side.
A friend of mine even got water to explode, some people are whizzards.