I'm measuring fatty acid species from serum with a Folch based extraction method followed by separation of neutral fatty acid species; cholesterol ester, triglyceride, free fatty acid, diacylglycerol, by TLC. TLC plates are visualized with fluorescein, dried, re-extracted, and transesterified before being run on the column (Agilent DB-225MS).

My main concern is these very prominent peaks that tend to turn up in every sample, no matter which species (intense peaks at ~7.7, 8.1 mins). The intensity of the peaks makes me believe I'm carrying over some chloroform/methanol which is contaminating the samples during extraction somewhere. (see runs of dilute chloroform-methanol).

Included a couple example runs, runs of dilute extraction solvents, a run of 23 lipid standards I use for calibration and integration of peaks, and a blank run which looks to show some bleed through of the very intense peaks.

Any help or tips would be appreciated.