Determination of Formic Acid by GCMS

[colin.fitzgerald87]

Hey All,

I have been spending a lot of time trying to determine formic acid concentrations from anaerobic cultures. I tried methylation and analyzed my samples by GC-MS, but realized my compound is still to small and comes out with the solvent peak. I then moved to HPLC (using prevail organic acids column with KH2PO4 buffer), I can see a nice peak for formic in my standards, but as soon as I add a culture supernatant I can not differentiate the peaks (I assume Na+ and Cl- in the media are causing problems detecting such a small compound). I have since moved to sylation and detecting on a Gas GC using an FID detector. I can see formic but it is shouldering off of the solvent peak. Any suggestions for better methods? I can provide more details about my methods if that would help?

Thank you,

Colin

[Johnny Rod]

Which GC columns were you using? What solvent(s)?

[jdezeeuw]

For FA, use thick film Rtx-1. 5 microns on 30m/0.32mm and use TCD.

if you need MS, connect a 5/0.25mm retsriction to the end so you can work with 1-2mL/min and normal pumps.

jaap de zeeuw, restek corporation

[Peter Apps]

I see formic acid as a nice sharp peak midway between acetic and propanoic acids on Restek PEG columns (RtxWax). The samples are wild dog urine and faeces, and so they have a multitude of bacterial fermentation products in them.

Peter

[jdezeeuw]

Peter, would you be willing to share a chromatogram of this analysis?

thanks
jaap

[Peter Apps]

No problem (as long as the link works !!)



Peter

[jdezeeuw]

Thanks Peter. This looks very good. What detector was used? It looks like MS. was this a 1 micron film on 0.32mm?

[Peter Apps]

Hi Jaap

This was a 0.5 micron film, 320 micron internal diameter, starting temp 40 C, programmed at 5 C/min. MS detection - formic acid is nearly invisible by FID.

Peter

[AICMM]

Solvent is methanol?

Best regards,

AICMM

[Peter Apps]

Hi AICMM

Yes, methanol solvent. We use it because it gives us the broadest range of extracted compounds form the wild dog materials. We are seeing diols and glycols that would never extract into the more usual non-polar solvents. I doubt that we would see formic acid with a non-polar solvent.

The anticipated problem with formation of methyl esters of free acids has not arisen - we always analyse within a maxium of a few hours of preparation and store at -18C. Also we do not dry the extracts (the samples themselves, except for anal gland secretion are air-dry before extraction), and I suspect that the traces of moisture inhibit esterification.

The only disadvantage is that methanol extracts urea and then gives methyl carbamate as an artifact peak.

Peter

[chromatographer1]

In case anyone would doubt Peter's results (a deed, foolish as it is unlikely), formic acid does elute where Peter says it does.

Twenty years ago I was startled to make that discovery.

Thanks for sharing your chromatogram, Peter. Don't trouble yourself in sending me any of those samples. I would hate to impose.



Rodney George

[Peter Apps]

In case anyone would doubt Peter's results (a deed, foolish as it is unlikely), formic acid does elute where Peter says it does.

Twenty years ago I was startled to make that discovery.

Thanks for sharing your chromatogram, Peter. Don't trouble yourself in sending me any of those samples. I would hate to impose. Hi Rodney - one of the reasons that we have the lab where it is, close to the wildlife areas, is the huge difficulties of shipping biological materials across international borders and veterinary red lines without having to do things to them like fixing in formaldehyde - which doesn't do the GC-MS results any good at all



Rodney George