Db-5MS for acetic acid?

[mowa68]

Hi all,

I am a student and am doing my first research project. This will imply analysis of acetic acid and propanoic acid by GC/Mass. This past few weeks I have read about acetic acid analysis on this forum and it seems quite difficult using GC. But before I ask for using LC/Mass instead I would like to make sure I cannot use GC.
The column is a db-5MS which is pretty equivalent to 5% phenyl 95%methylpolysiloxane (non polar, low bleed).
After consulting literature and this forum I would choose THF as solvent is that a good choice?
I really don't want to ruin the column so if you think it is too risky I'll convince my supervisor to use LC.

Thanks!
M.

[Don_Hilton]

These can be analyzed by GC, but with the column you wish to use the samples should be derivatized. Underivatized on a 5% phenyl column, organic acids give poor peak shape.

THF can work. The question is what else is in the mixture. Are you extracting the compunds from a matrix or are you disolving the entire sample. What concentration range are you looking at?

[gstaepels]

A principle in chromatography is "like likes like". Thus polar compounds are best analyzed using a polar phase column. The analysis of carboxylic acids are not problem if you use a FFAP type column. The peak are sharp and symetric. You could use a WAX (Polyethyleneglycol) as well but FFAP works better.

Hope this helps

Gilbert

[chromatographer1]

You supervisor will want you to review the techniques for acetic acid and will expect you NOT to waste time on an analysis which is likely to give you erroneous answers and that will be a waste of time and equipment.

Unless you can make an ester of some sort and separate the acetic ester from the reagents and your matrix you are better off using LC or IC to make your acetic acid determination. One does not need and perhaps should not use LC-MS for this analysis. Acetic acid can be done using a RI detector by LC.

best wishes,

Rod

[GasMan]

I can back up the comment that gstaepels makes, good sharp peaks for the carboxylic acids using a FFAP column.

Gasman

[chromatographer1]

The problem with HoAc lies in the equilibrium of state, the matrix absorption in the injector, and the necessary requirements of inertness throughout the system. Getting the free acid to the column is the hard part. Eluting the acid after it gets on the column is the easy part, but hard part is called hard for a (several) reasons.

best wishes,

Rod

[mowa68]

Thank you all for your replies!

I checked and we have no polar column for GC.
I think I cannot do a derivatization because I already have a mixture of ester and alcohol with the acetic acid.

I am now considering LC and eluants to use with a C18 column (the only one there we have).
@Rod : why wouldn't you use LC/MS please?


Hope it'll work because otherwise the project will be dead...
Thank you all again!

NB: I wish FFAP column was cheaper because it, indeed, seems to be the perfect one for this study!

M.

[Johnny Rod]

Look up some derivatisations for organic acids. providede you don't have too much water in there then you can make a different ester to the one in your sample. As said, GC of free acids is a pain in the backside, but GC is likely the best technique depending on the sample conc, or HPLC wity RI as Rod says, depends what you have access to.