GC/MS Analysis of formic acid from hydrothermal reaction

Discussions about GC and other "gas phase" separation techniques.

4 posts Page 1 of 1
Hi all,

I am new on this forum and hoping for some advice! I am performing high temperature water reactions with carbon dioxide and want to observe formic acid via GC/MS over HP-Innowax column with an autosampler. My samples have no solid residue (I filter them three times through 0.22 um membrane) and are in water. I have observed decent peaks for most products (eg acetic acid) but not for formic acid as I suspect it requires acidification to pH 3, but am hoping for further advice as I have never acidified samples before. Do acidified samples run through headspace analysis, or is it possible to analyse the liquid phase?

I know GC/MS is not ideal for formic acid analysis, but unfortunately this is the only analytical equipment I have access to and I want to try to make it work. I also want to avoid derivitization.

I would really appreciate any advice! Thanks!
What concentrations do you expect in your samples? If trace, this may not work but if the concentrations are pretty large you might try this.

If it were me, I'd do whatever I could to do this using headspace sampling. You probably don't want to start injecting a bunch of mineral acid into your GCMS. If your analytes are in an essentially a pure water matrix, perhaps acidifying them and saturating them with salt before a headspace analysis will get you where you want to go. If the gaseous injection isn't sensitive enough, you might try solid-phase microextraction.

The other approach that isn't too much more complicated is to acidify them, saturate them with salt, and extract them with a clean organic solvent (like methylene chloride) and then inject the dried (over anhydrous sodium sulfate) organic solvent. For direct injection sampling, all is better when you can inject organic solvents and not water.
I agree headspace. You can either analyze it as native formic acid or pick an alcohol of your choice and analyze the ester.

I use in tube esterfication for short chain fatty acids.
20ml headspace tube
5ul sample
5ul Concentrated H2SO4
10ul alcohol
incubate 120 deg C for 60 minutes and sample. Use an internal standard like 4-methyl pentanoic.
Hi both,

Thank you for your very useful responses! I will attempt them and post my results.

All the best!
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