I reconnected the column, and retention time changed!

[zimanli]

Greetings,

I bumped my column out of split/splitless inlet. I reconnected the column back into my inlet and run a standard sample. the signal is smaller and the retention time changed. Please help. What does this demonstrate?

Thanks a lot!
ziman

[chhubert]

What instrument are you using? For Agilent GC, the column should protrude 4-6mm from the ferrule. Any big deviation of this length may result in reducing signal. Second, how significant the retention time shift when comparing to your previous one? Inlet leak, say from the septum or ferrule causing a reduced flow rate?

[chromatographer1]

Since the retention time changed the flow of carrier changed in your column. Did you have a leak? Or did you create a leak. Since you do not wish to tell us the difference in retention time, how are we to know.

Placement of the tip in Agilent GCs does affect the linearity of the split which may appear to reduce or increase the size of any single peak.

Was the column not properly sealed initially, which allowed you to 'bump' or BREAK the column at the inlet? Your split ratio and linear flow rate would change enormously if you were leaking around the ferrule at the inlet.

best wishes,

Rod

[zimanli]

Hi guys, the retension time changed from 5.939 min to 5.890 min. and the peak area droped from 4e6 to 1.3e6. the base pressure is the about the same. (from 5.8e-6 to 5.85e-6 Torr)

[zimanli]

Could that small shift in retention time be due to the change of Column length? I trimed about 15 cm off. thanks a lot!

[chhubert]

What is the column length? If your column is of 30m long, I guess the retention time would not drift too much after cutting 15cm. Shorter column may however pronounce the drift.
What is the compound that you are analysing? There are heap of reasons on dropping sensitivity after columin installation, for example wrong installation of column; wrong column cut; exposure of fused silica fragments into the column during cutting column, causing absorption of analyte, etc.

[zimanli]

I took off the column from the inlet and found out that there should be a LEAK. My column could even slide through the graphite ferrule. And the column extended out about 1 in of the graphite ferrule. I guess I tightened the nut way too loosely.
I got normal peak area again. It is just the retention time(5.888min) is still a little bit smaller than what it was(5.939min).

thanks

[Peter Apps]

Hi Ziman

The "change" in retention that you report is too small to be significant.

If you are trying to troubleshoot retention time changes the important pressure is the one in the inlet, not in the mass spectrometer, and the whole idea of having a pressure controilled inlet is that the pressure does not change very much when there is a leak. You cannot troubleshoot gas sytems effectively by looking at pressure readings, you have to have a leak detector.

Haven't we talked about this before ?

Peter