Since these are "volatile" fatty acids, then you can easily condense them on a cold metallic or ceramic surface. Take measurement of the condensation surface before and after the condensation and estimate the difference in weight and this will give you the amount of produced fatty acids from the fermentation process.

Hope this helps answer your question.

Professor Yehia Khalil

Yale University

USA

To my knowledge, the best method is to use a GC equipped with a flame ionization detector and a capillary column (for example Agilent HP-FFAP or similar, 30 m long, 0.53 mm inner diameter) with a gradient temperature program from 105 to around 150 C. Nitrogen or Helium can be used as carrier gas. You can directly inject (acidified) water based samples. 

Dear Javad,

we determined Volatile acid and ethanol by GC analysis, using a Shimadzu GC-17A equipped with a FID detector and a capillary column with a PEG stationary phase (BP20, 30 m by 0.32 mm i.d., 0.25 μm film thickness, from SGE). Samples of 1 μL were injected with a split-ratio of 1:10. Helium was fed as carrier gas with a flow rate of 6.5 mL/min. Injector and detector temperatures were set to 320 °C and 250 °C, respectively. Initial column temperature was set to 30 °C, kept constant for 3 min, followed by a ramp of 10 °C/min till 140 °C, then kept constant for 1 min.

Sincerely,

gaetano

A first step of methylation is necessary to analyse fatty acids by GC-FID using a polyethylene glycol column and temperatures between 140 and 200 ° C. The methylation used is adapted by Bligh and Dyer method using 600 microliters of a 2N solution of potassium hydroxide in methanol.

Dear Ludovica,

Are you sure that are "volatile" fatty acid? 

In your case you analyze methyl esters....or Fatty Acid Methyl Esters.

Sorry for my doubt, 

gaetano

Fatty acid methyl esters