In anaerobic digestion experiments we have used our Varian GC-MS exclusively for biogas analysis but I know it is capable to do much more, also for assessing various interest organic compounds in slurry (mainly volatile fatty acids). I read in some articles that researchers do this simply by injecting a filtered sample. I suppose part of the interest components will be retained/lost on the filter. Specialists said that I must extract the interest compounds prior to analysis but not use the raw sample (filtered or unfiltered). Is there any protocol or accepted method for analysing slurry samples by GC-MS? Thank you.
Carmen,
For fatty acids you can make a 1) homegenization 2) saponification/methylation (to convert your fatty acids to methyl esters) 3) extraction to dichloromethane. Such extract you can analyse for FAME. For quantitative analysis for such compex matrix you can use a standard addition method
For screening of VOCs you can make a static (or if you have an instrument) dynamic headspace analysis, after that you can focus on some other groups of compounds (you can check my papers about this topic)
regards,
G
Thank you Mr. Boczkay, I will check your papers in this topic. I admit that I am more confused now, after your suggestion to do saponification, extraction etc. I referred to VFA that are short-chain fatty acids (methanoic acid C1- pentanoic acid C5), they indicate the anaerobic digestion good/bad balance towards methane generation. Should I understand that injection of raw filtrate is not indicated for slurry samples? I must search some more papers about this.
Regards.
Ahh, ok - for VFA you don't have to make the methyl esters. Check this paper for some examples
http://www.wseas.us/e-library/conferences/2009/lalaguna/EPREWA/EPREWA77.pdf
Direct injection of filtrate is not the best choice (you will retain in the liner and at the top of the column the non-volatile compounds, salts etc.), but for 2-3 injections you can try - at the end if you will find any loss of resolution just cut off 10-15 cm of front of the column. Remeber to lower the pH to acidic to obtain the acids in non-diisociated form.
Better choice is to use a static headspace (SHS) or SPME-SHS.
regards,
G.
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