GC-HS non retained "ghost peaks"

[GT]

Dear all,
I'm analyzing by means of GC-HS the residual solvent content in Active Pharmaceutical Ingredient with the following parameters:
HS Agilent G1888, GC-FID split mode, Solvent NN-DMF, column DB-624 0.32, 30m, 1.8um.
The problem is that when I analyze blank of DMF or standard solution (that is DMF with low level of volatile solvent like methanol, ethanol...) I obtain a good chromatograms with very small peaks at the beginning of chrom. (same RT of unretained compuond like propane), but when I analyze my samples I have at least 2 big peaks at this RT. Even if I chenge tho polarity of my column (DB-WAX) I can see the same situation.
Are these peaks due to system or they can arise from my sample?
All explanations will be usefull
Thanks

[Peter Apps]

If the only thing that you change is the addition of real sample then the peaks must come from the sample.

I am assuming that you can replicate the findings, and that you are not consistently running the real samples just after having run a concentrated standard.

These are very unlikely to be ghost peaks, which are due to the elution of material that was injected in an earlier run.

Peter

[GT]

Peter,
thanks for your reply.
Your assumptions are correct: after standard I always run a blk with no peaks at the beginning of chrom. and GC oven cycle goes up to 190 °C for 5 min. to avoid carryover from one injection to the other.
But if these peaks are from my sample what could they be ?

[Peter Apps]

"But if these peaks are from my sample what could they be ?"

You are analysing for residual solvent....... does that give you a clue ?

Peter

[chromatographer1]

Yes, Peter is quite right.

You said you were performing an analysis:

"the residual solvent content in Active Pharmaceutical Ingredient "

Ask your supplier ( manufacturing section at your site? ) what solvents do they use in making the the "Active Pharmaceutical Ingredient"

How are we to know what you are seeing? It is volatile solvent(s) that elutes near propane from what you have told us. It is time to start running some 'marker solvents' and find out what you are seeing.

Good luck in measuring and identifying the solvent. Need help, please ask your questions. Many of us are glad to assist you.

best wishes,

Rod

[GT]

Hy Rod,
I can see easily all the solvents used for preparation of API (ethylacetate, methanol, methylformate and so on) but from my experience I have no idea of which unknown solvent could be so in front of chromatogram.
What are "marker solvents" ?
Thanks very much.
GT

[chromatographer1]

Marker solvents are solvents you know are in the process such as
"ethylacetate, methanol, methylformate ".

Since these are unknown peaks among the known peaks in your sample and since they are extremely volatile you must look at the chemistry of your sample, the process in producing your sample, and determine what if any volatile can arise.

You could run your sample using a PLOT porous polymer to determine if you can identify these as methane, ethane, ethylene, H2S, CO2, or some other analyte such as dimethyl ether or methylamine.

If they are not in your solvent standard then they arise from your sample not your system.

Isn't chemistry fun ?

good luck in determining the idenity of your comtaminants.

Rod