GCMS analysis of Butyrate, Propionate and acetate

[csang]

Dear all,

I'm facing some problems in analysing my samples for short-chain fatty acids (SCFA). I have never worked with GCMS as such I have sent the samples to an external lab together with the internal standards.

I was then told that the three samples are probably too volatile as such it was not detected at all. Does anyone has any suggestion or is there any reference material for SCFA analysis anywhere? I'm looking for a quick way to analysis them since it is only some preliminary work and I can't spend too much time on it......

Thanks in advance

CS

[skunked_once]

It's not clear from your post whether the problem is the GC method for the free fatty acids or just a problem with the MS detection. If you need a GC method, log on to "chromatography.com" and do a search for your compounds. You will find several examples of applications.

[chromatographer1]

The problem in the method for SCFA Ester analysis is the volatility of the esters, especially the methyl esters.

A freshly prepared solution of trace amounts of these esters will volatilize into the headspace of the vessel in which they are contained and when you open the vial or vessel to sample them.............whoosh...... they are gone.

After esterification and extraction of the free acids it is usually necessary to have NO headspace in the vial and to keep the vial below 5°C if possible Sampling through a septum is advisable but rubber septa can absorb esters and ruin the measurement.

Methyl Formate boils at 35°C. Imagine the vapor pressure at room temperature !

[skunked_once]

Aha! You are preparing the methyl esters which makes them even more volatile. Do you have to follow that method? These short-chain fatty acids can be analyzed directly on a GC column without derivatization. This would eliminate the derivatization step and reduce the loss of the fatty acids due to volatility. The free acids are still volatile (and smelly) but this should be easier.

[chromatographer1]

My assumption was that the acids were derivitized.

No one would try to run a free acid into a MS with all that bare metal exposed.