Low GC Signal for MeOH std run

[waiwai]

I am using a HP6890 Series GC. I am currently using a Porapak-Q column, using a FID detector.

Recently there have been several problems with my Methanol standard run. Originally, there was just bad tailing as the tailing starts at the mid of the peak. Then, i have sonicated the FID jet, the collector body and its insulators. Then I started conditioning my column again. The signal would go up till around max 70 and after igniting and increasing our column temperature, the signal will go to as low as 2- 4.

I'm not sure what's the cause of this as I have checked the injector, the liner and fid jet.

[chromatographer1]

waiwai

You tried to give us enough information to help you but there are so many details missing ...................................

Tailing is caused by actives sites. Where have your actives sites originated?

Methanol std? conc , matrix, solvent?

What has been injected onto your Porapak Q column?

After you first installed a porous polymer column and conditioned it to remove most of the chemicals present from its creation, there is no phase to bleed off. Conditioning is not required UNLESS you have put onto the column material that is highly non-migratory. Have you done this? Have you backflashed non-volatile sample into your pneumatics at the inlet?

If you have done either, then try to remove the contaminated glass wool and polymer packing at the head of the column (several inches if possible) and clean the glass tubing. Repack the column but leave 4-6 inches empty at the inlet after you insert the glass wool. If your sample is aqueous this is especially helpful. You can insert additional wool at the inlet which will give surface area for any non-volatile materials to collect. This will make it easier to remove them later. Also clean your pneumatic lines if you can.

If the column is too contaminated you will have to replace the column. It is possible to repack your own if you are knowledgeable in such matters.

Of course, your problems may be traced to a simple leak, the septum or around the ferrule holding the column in place at the inlet.

Good luck and if you can share more information about your sample I will try to give better advice.

best wishes,

Rodney George
consultant