Chromatography Forum

Dears
I have new Grestel GCMS (Grestel TDS, GC 7890A, MS 5975C) and I load method with SIM scan mode, which I always used to do with old GCMS (GC 6890N, MS 5973).

My problem that the Ions 135 and 136 and some others which appear OK in the whole Oil GCMS in old system did not appeared in the new system. I received only baseline with no peaks. Could any body help me in this.

1) have you been able to see peaks on any sample on the new GC/MS?
2) how are you introducing the sample in the new GC/MS and how were you introducing it on the older system?

Sir
First let me thank you very quick reply.

I can get most of the peaks i know in other ions like 191 and 217, 245, 231. But not in 135 and 136 and some others.

The sample is injected by the Grestel in the new system. You add the oil or rock sample to a tube that thermally cracked in the Grestel machine and then injected automatically to the GCMS.

The old system the whole oil is injected directly to the injector by the syringe of the auto-sampler

It is possible the components that gave you peaks with 135 and 136 ions are decomposed by the TDS. I would check that with a manual liquid injection into the new system, assuming Gerstel left you with a functioning injection port. Or perhaps inject the liquids into a blank TDS tube, though if decomposition is the issue, it may still occur.

I have an old purge and trap setup that bypassed the inlet back when that was a common thing to do - in that case I have to put the liquid standard directly on to the trap, then go straight to desorb when troubleshooting.

As Yana001 points out, you may be decomposing the sample -- or you may be failing to transfer all of the sample to from the TDS to the GC inlet. Temperature is important. You do not give instrument conditions, so we are not able to pick out anything that might be a problem. And kowldege of the material in the TDS tube or compunds involved might help.