Chromatography Forum

Not sure what is causing my problem here... I am running a "tried and true" GC-MS method on a Varian 1200L triple quadrupole MS. A few weeks ago the peaks looked fine, however I did have to vent and cleaned the ion volume at that time.

Since then, I have approximately the same sensitivity and peak shapes for the first 5 analytes in my text mix. The remaining 4 analytes (which elute >200C oven temperature) have very bad peak shapes. They look like hills and are very broad. At first I thought it was an injector issue, so I replaced the liner, it still looked bad. Checked purge flows, all is good. Absolutely nothing in the method parameters have changed, and these 4 peaks used to look awesome. I still wondered if there was an active site in the injector, so I baked it out and it still looked the same. I then tried a Uniliner in the 1177 injector to minimize contact of the 1uL injection with metal parts in the liner. The last 4 peaks still look very bad. I then replaced the analytical column with a brand new equivalent, and the last 4 peaks still look the same - bad.

There is approximately ~0.5 meters of Restek 0.25mm ID Siltek guard column installed into the MS. I use a presstight connector to join the analytical column to guard column installed into the MS. I have replaced this presstight several times recently to try and resolve the problem to no avail - clearly it's not the problem either. It's guess it's possible I have a bad cut on the end of the guard column installed into the MS. I was wondering if anyone thinks I may also have a dirty ion source that only seems problematic with the higher boiling point analytes? Would that make any sense? The chromatogram baseline looks good with good spectra and peak shapes for the first 5 analytes in my 9 analyte mix. I have increased the source temperature from 200C to 300C for several hours, and also tried running my test mix with the source at higher temperatures (225 and 250) with the same bad results.

Thanks for any suggestions!

Chromatographydude,

Are the retention times of all of the components, even though the later are broad, the same as before? Are the laters' reactive? What id of column are you using and how much are you shooting? Why are you using the 0.25 guard column on the detector end?

Best regards.

It's more likely residual contaimination in either the soruce or transfer line or both. Clean them thoroghly, not just ion volume. Before do that, you can run a full scan without injection and column to see if you can find residual ions of the last 4 compounds. good luck.

Injection ports can become active over time. I have to solvent wash mine every once in a while using a brass brush. When things act as if the front end is active and a new liner changes nothing. How old is your column? They are consumables.

Caution if you solvent wash contact Varian for instructions. I use Agilent systems and they have washing instructions on their website.
You don't want to get solvent in the EPC controller!

Thanks for all the responses... Just to follow up on what I found to be the problem, we had recently switched the GC connected to our MS. We had to modify the transfer line hole and turns out I didn't have them pushed together far enough - there was an obvious "cold spot" in the transfer line where it wasn't pushed into the GC far enough. Problem solved!