Chromatography Forum

1) The peaks on the first GC are at the same residence time and area, but have broadened to close to twice their normal width. A new column didn't fix this.

2) The peaks on this GC are at the same retention time, but are much smaller (height and width) and have an echo that is maybe 10% as large.

Both are using a 50uL injection loop, helium carrier gas (30CCM), packed column...

Any thoughts?

Thanks

Please post more information.

1. What GC's are you using.

2. What columns are you using.

3. What is your sample and what are the peaks that give the problem.

4. GC conditions.

Gasman

1) Varian 3800: Hayesep DB 100/120 (packed column)- H2, N2, CO, CH4, C2H6 - the sample is various mixtures of those - the injector is at 150, the column starts at 40 for 12 minutes then ramps slowly to 220 - the detector temp is 250 with a filament T of 290 - 30 CCM column and reference gas rates

2) Varian 3380, all else the same

We tracked down one of the problems on the 2nd GC: somehow the filament T had been set down to 0. I returned that to 290 and the peaks are normal size, though there are still the "echo" peaks about 10% of the original about 20 seconds later...

Your echo peaks are from your sampling valve.

Change the timing of the valve and see if the retention times of the echo peaks changes accordingly.

More specifically, change the setting of the time of the "return to fill position" .


best wishes,

Rod