Chromatography Forum

Hello to you all! Is there anybody out there giving me some suggestion? I write from Italy, where I work as research assistant at ENEA research institute.
I'm just approaching to the GC world, I'm currently doing GC determination of N2O (RT=1.7 min) with a Varian GC 3300; I use a 2 mt.Porapack Q (80-100 mesh) packed column, kept at a 40°C temp., while the injector is set at 100°C.
Since some weeks, I observe two ghost peaks with RT = 0.40 and 14.00 min, respectively. The first one is very tight and defined, whereas the other one is broader. I replaced the column and the septum but the problem has remained;furthermore, I noted that the two areas are proportional to the injected volume. That led me to suppose that the problem is due to an injector contamination, so that's the question:

1) Am I right?

And if so:

1) How to clean the injector (An "on-column" one)?
2) I read on internet that it is possible to eliminate impurities fro the injector simply disconnecting it from the column and increasing the temperature up to 350°C for several minutes; does ir risk to damage the injector?

Thank you all for suggestions

Max

Your ghost peaks are reproducible... this suggests that you have some contamination coming from somewhere... I dont think burning off your column is going to help too much, because if it was column contamination, i am not sure the peaks would be as reproducible as you are seeing. This suggests that yes, it may be your injector, or it could be coming from your sample preparation. GC is quite sensitive, so any contaminated glassware or laboratory utensils could have quite a significant impact on your separation... The fact that the areas are proportional to the injection volume could also indicate some kind of contamination in the sample....?

I could be wrong, but thats what came to mind.

I hope that this helps.

Chel x

Thanks for suggestion, Mr or Mrs!
I think I got it: ghost peaks are due to oxygen (the first one) and water (the second one, the broadest). I tried to modify the run set-up:no results, with a higher column temp I had a better definition and a shorter RT, but N2O peak was undistinguishable from O2 one, and with a colder temp the run was really too long. I've decided to search for another column, a longer one or packed with a different material, do not keeping water stongly. I was told to try Porapack P instead of Q, or Porasil. Also, I've been suggested to use a capillary column, but I would prefere to avoid, too expensive! Have you got another suggestion?

Thanks a Lot

Max