Fatty acid ghost peaks

[Rmahat]

I have been working for a while in bacterial Lipidomics using Thermo Trace DSQ II. All the sudden I started seeing ghost peaks in system blank corresponding to C16:0 and C18:0 fatty acid, underivatized. Since my sample had them, I first gave doubt to the liner after condensation test and changed it. However, it did not solve the problem. I have already changed new inlet house (whole inlet) but the problem is still on. I've installed everything new (liner, graphite seal, sonicated septum holders/ plate, silver seal, and terminal fitting. Tried with new column also and column has no contamination). I was using Merlin septum when I first noticed the problem and the ghost peak intensity was close to 2x10^6. When I tried using a BTO septum (preconditioned) at all new inlet set at 200 C the ghost peak is so worse. It reaches around 10^8. When I use methanol as last syringe cleaning solvent these peaks convert to corresponding FAME on air blank. And, worst part is when I inject BSTFA blank I can see TMS esters of C12:0 to C18:0 fatty acids. I have come up to the tentative conclusion that these septa bleed fatty acids (found a substantiating literature also: http://chromsci.oxfordjournals.org/cont ... l.pdf+html) assuming carrier gas is contamination free (Checked carrier gas too. Condensation test points to inlet). Has anyone encountered similar situation? Share please, I may have been barking the wrong tree........

[Peter Apps]

The publication that you link to does not mention FFAs from septa (in the abstract at least). The most likely source of these two FAs is fingerprints.

Peter

[Rmahat]

@ Peter Apps

Please look at table II. No, I have been very careful about my fingerprints. I wear clean cotton gloves all the time during changing/ handling parts in inlet or column

[Rmahat]

......and handled septum and liner with clean forcep

[Peter Apps]

The fingerprints could be anywhere; glassware, syringe needle, paper tissues, vials ...... And they do not necessarily have to be your fingerprints. Exclude or change things one at a time and see what makes a difference.

Strictly these (and all the problems in the paper that you link to) are contaminants, not ghost peaks. A ghose peak is one that appears in a later run than the one in which it was injected - it is called a ghost because it comes back form a previous life so to speak.

Peter