Chloroform GC-FID contaminating peaks? - (May/02/2014 )

Hello all,

I was wondering if anybody has come across this anomaly when extracting lipids using the standard Folch protocol.  Having removed the chloroform phase, I evaporated it to dryness at 37oC in a vacuum evaporator and derivatised the resulting pellet to FAMEs for GC-FID analysis.  Amongst the expected FA peaks, I got these 3 contaminating peaks at 1.789, 2.896 and 3.027.

I repeated the process without the sample, so just chloroform:methanol, removed chloroform phase, evaporated to dryness and while no pellet was present, I used the tube to mix the reagents for FAME derivatisation.  I got the same 3 contaminating peaks at 1.789, 2.896 and 3.027 (see attached - peak at 9.815 is methyl behenate).

I have discounted contamination/issues with the column, GC system, FAME reagents, hexane etc.  The peaks were evident for 2 separate chloroform batches and were not present when chloroform was run directly on the GC.  The system is an Agilent 7890A with a DB-23 column.  

My best guess is that they are contaminating artefacts in the chloroform or from the plastic eppendorfs used during evaporation (I know plastic is generally considered a no-no with chloroform but it was only used during the evaporation stage and the peak at 1.789 is so intense that I find it hard to believe that there would be that much interference, given that detection is with FID and not MS - although maybe I am wrong?!)

Does anybody out there have any thoughts or suggestions or have had similar experiences?  I could just ignore the peaks but I would rather know what's going on!!

Thanks in advance

Jaff

Can this be by-products from the derivatisation? And you should use glassware to exclude issues with the plastics.

the contaminants are most likely from the plastic but may also be extracted from the methanol (or both).

have you tried injecting methanol?