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