We are experiencing severe palmitic acid contamination when the step of saponification is involved in the sample preparation procedure. The fatty acids are quantified by GC-MS after their silylation. If we are analysing pure fatty acids standards there is no sign of contamination and calibration graphs are good passing through the zero. I wonder if anybody has experienced the same contamination problem conducting fatty acids quantification and found the remedy.

I work for a soap company, and we always have some palmitic acid and stearic acid peaks on GCMS when we inject a trimethylsilyl-derivatized sample. We feel this is from built-up contamination in our inlet, liners, and head of the column from numerous injections of extracts of bar soap samples. Just yesterday I offered the option to a technology scientist that we could clean this out real well then use a new dedicated column for his experiments if need be. We have also injected blank derivatizing agent several times before running a real sample so we can ascertain whether the fatty acid peaks are real.

Hi Molever,
Thank you for your reply.
Actually we detect all the main fatty acids in blank. We currently setting up the method and I believe that contamination is coming from glassware or plastic ware we are using. The contamination is very high so that it is impossible to do quantification. Now we are tracing the source of contamination. It can be the detergent we use for glassware washing, in spite of the fact that before using it for fatty acids analysis we wash it with "chrompix" (potassium dichromate in sulphuric acid) or plastic tips we use to add reagents and so on.
I wonder if you have some idea about the possible source of contamination and can tell us about general precautions during sample preparation you usually follow, which perhaps we are missing now.

Let me begin by asking a dumb question, actually two questions: what exactly are you trying to measure, and in what matrix???

The method is intended for binding media determination in art objects (paintings).

Could it be that your saponification is incomplete and that you are accumulating lipids in the injector which are then derivatized when you inject sample? I am not familiar with the sylilation technique so I am basing the suggestion on our experience with transesterification of lipids, in the injector, with methylating reagents which supposedly do not transesterify.
Actually one would need more info......

I quite agree, much more info is needed. I suspected that a std or some other sample was flashing back and depositing free palmitic acid which then was derivitized when the sample dissolved into the reagent was then injected into the port.

But that was too obvious I thought. And soap FA salts can be swept into the sample preparation, but with the meager details given it is quite difficult to suggest answers, but good luck anyway.