Residual Formic Acid and Acetic Acid

[stevel]

Hi All--

We need to develop a GC method for the analysis of residual formic and acetic acids in a product. (Limits are 5000 ppm each) I've tried direct injection on DB-FFAP and DB-Wax columns. We're having trouble getting any measurable response for formic acid. Acetic looks ok for a few injections, but peak shape degrades after that. (flame-ionization detection)

Does anyone have experience with GC analysis of these acids? I assume some derivatization procedure will be necessary. I'm looking for the best one.

[Consumer Products Guy]

How about HPLC with conductivity detector and column designed for organic acids? That's where I'd start.

[dave750gixer]

In the past I found that when analysing residual solvents on a DB-624 column, any acetic acid present gave a very poorly shaped peak with very variable retention. When the samples were made up in tetrahydrofuran the acetic acid gave a vey nicely shaped consistent peak.

The only reason I found this was that I was working in a chemical plant and would make up plant troubleshooting or environmental monitoring samples in a solvent that could not come from the plant. I therefore kept a list of solvents that we did not use on plant and couldnt be produced in any of the reactions.

[dave750gixer]

Sorry, forgot to add that this was with a FID

[chromatographer1]

You will not have much response for formic acid with a FID, ie almost none.

Your recoveries of the acid will be difficult if you are injecting solutions which contain your matrix (I assume it has a basic nature or functional group).

The best solution is Ion Chromatography. Lots of standard methods are available from vendors with published articles.

Sometimes you can do low levels of HoAc and Formic acid by NMR. It has been done. Been there done that.

good luck,

Rod

[Peter Apps]

If you cannot do ion chromatography you could try derivatizing to butyl esters.

Peter

[AICMM]

Stevel,

Not surprising that formic acid gives poor response due to similarity to formaldehyde. Have you considered methanizing or even O-fid? I know of at least one application that is done this way for formaldehyde and you might be able to reasonably easily convert your GC to such operation. Regarding peak shape, good luck. I would really like to hear how this turns out.

Best regards.