Chromatography Forum

Recently my GC keeps showing a large ghost peak. It only shows in the first run of the standard solution in the beginning of the day. In the subsequent standard and sample run, the ghost peak disappears. It sometimes appear again in the middle of the day when standard is run again and subsequently it is gone again.

I am using a PE Clarus GC with single injection splitting into 2 columns namely DB 1701 (which goes into FPD) and DB 1 (which goes into the NPD). The ghost peak appears on the NPD only.

We have done everything possible eg. changing the standard solution, changing the retention gap, changing the syringe, cutting the analytical column, changing the Y-splitter, changing the liner, changing the ferrules, changing the liner o-ring , cleaning the injector port. Ghost peak still persist. The same standard ran on other instruments with the same configuration is OK.

Fellow chromatographers out there please help me.

Hi Leon,
Is your other GC exactly the same configuration?
On initially looking at your post it sounds like septa peaks which accumulate overnight/idle and then appear in your 1st GC ramp.
They may be detected by NPD and not by FPD.
Do you use the same septa on the other GC?
I admire your determination!
Good Luck
WK

Try a run without injection,on the beginning of the day,see if the peak occur.
It may be contamination of your gas line accumulating during the night at the front of the column,or septa,but i you have septum purge it should not be an issue.

Bye

try switching the column outlets, keeping the inlets the same. See if you see the ghost peak from gases from the other injection port. That will tell you if it is common to both inlets.

Hi Leon,
Is your other GC exactly the same configuration?
On initially looking at your post it sounds like septa peaks which accumulate overnight/idle and then appear in your 1st GC ramp.
They may be detected by NPD and not by FPD.
Do you use the same septa on the other GC?
I admire your determination!
Good Luck
WK

Hi WK,

We have 3 other PE GCs with the same configuration but different column combinations. All are OK. Septums used were the same. Seems that the ghost peak appear after run is stopped for some time.

Thanks

:idea:

Try a run without injection,on the beginning of the day,see if the peak occur.
It may be contamination of your gas line accumulating during the night at the front of the column,or septa,but i you have septum purge it should not be an issue.

Bye

I guess you could be right that it is an accumulation. Since there's septum purge, i really don't know where the contamination is coming from. I will try out your suggestion. Thanks.

Leon,
I leave my Autosystem at 80degC overnight with 1ml/min flow and split 20:1. I still have to run a blank ramp first to clear material that has "condensed" on the column.
(Presumably if I left the split at 100:1 I would have approx. 1/5 of the material condensed as I have now - but waste expensive gas).
Have you used the problematic Clarus for splitless work and overloaded the injector? - since xxx might be right about slightly contaminated carrier gas line - in which case you are lucky that it doesn't occur in every ramp.
WK