Inlet contamination

[pete_hops]

Hi All
I have been trying to diagnose an issue with a CIS injector on one of our GCMS instruments. The symptoms being contamination appearing in a run, even when a run is initiated with no injection performed, (running in split less mode, isothermal inlet temperature) as well as a loss of higher molecular weight compounds in our test mix. When we run an undiluted sample of the same test mix, in split mode, the chromatography is restored to what we would see normally, however the contamination is present just not as prevalent. So to me there seems to be active sites within the inlet which are causing the loss of the higher molecular weight compounds, and perhaps this contamination is related/cause of them. The liner has been changed, and no improvement has been seen.

The instrument is using a shared Helium, and the contamination is not seen elsewhere. The septum less head has been cleaned with 3 solvents DCM, acetone and methanol, and sonicated in each for 30 minutes each time. The ferrules, needle guide and syringe replaced has been replaced and the contamination is still present.

The GC has a split/split less inlet installed, injections have been performed with it, and this inlet does not display these issues.

[osp001]

Have you tried heating the inlet to cook off potential contaminants?

[pete_hops]

Hi osp001

Thanks for the suggestion. Heating the inlet showed some positive signs with the contamination becoming less severe on the first run after heating. However it returned to previous levels on the next run. It appears (at this stage) that the contamination may be in the split line where it joins the inlet, as this was one area which was not chemically cleaned. After cleaning here the contamination has reduced and is reducing on subsequent runs.