Chromatography Forum

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........

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

@ 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

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

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