Shifted retention times GC-MS/MS

[Remu]

Hye

I am working with PAH compounds and to protect our analytical column we added the retention gap with the glass press-fit connector. After that all the retention times started to shift approx. 0.5-3 min. Every run is different so we can't change the retention time windows either. Do you have an idea what could be the problem? We did already the inlet leak test, but it's ok. Is it a leak problem concerning the joint between the columns? Thanks for your help!

[larkl]

I'd sure check for a leak. Do you have a leak detector? Wouldn't take a minute to check around the press-fit.

[Peter Apps]

A leak sounds likely, have the peak areas changed ?

If you can't find a leak, another possibility is some kind of strange solvent effect on the retention gap. What are the lengths and diameters of the retention gap and the column ? What solvent are you using, how much sample do you inject, split or splitless, what is the oven programme start temperature, and what kind of deactivation does the gap have ?

Peter

[Remu]

Thanks for the quick response! Unfortunately we don't have a leak detector . We ordered a new column connector which should be leak free and easy to use. Let's see if our problem with retention times disappears.

Our analytical column is 0,25*0,25*30(m) and retention gap 0,32*0,25*3(m). We inject 2 µl splitless hexane or toluene. The starting oven temperature is 80 C and deactivation process is a phenyl methyl deactivation.

I'll wait now for the connector and will answer then does it help or not.

[Peter Apps]

Under these conditions I would expect recondensation with toluene, and probably not with hexane. Are the retentions longer with toluene as solvent ?

Peter