Condensation test for GC- help needed

[juniorchem]

I want to do a condensation test in my GC to see whether the cause of a number of ghost peaks in my chromatogram is injector contamination.
The agilent manual says the procedure as:

"Leave the GC at 40-50�C for 8 or more hours.
Run a blank analysis (i.e., start the GC, but with no injection) using the normal temperature conditions and instrument settings.
Collect the chromatogram for this blank run.
Immediately repeat the blank run as soon as the first one is completed. Do not allow more than 5 minutes to elapse before starting the second blank run.
Collect the chromatogram for the second blank run and compare it to the first chromatogram."

I havent done this yet. So I want to make sure I dont do anything wrong. If I run the GC for like 8 hours at 40 deg celsius with air injected that makes the first run. But for the second run also, do I need to run it at 40 deg celsius for another 8 hours again? Or am I wrong?

Thanks for any help

Regards

[aldehyde]

No, you repeat the run immediately after the blank run finishes to see if you get a) ghost peaks in the first run but not the 2nd or b) ghost peaks in both or c) ghost peaks in none.

a indicates something is being cold trapped on the column and eluting first oven ramp after idle

b indicates some sort of constant contamination like a plugged split vent line

c indicates something to do with your injection.

[juniorchem]

Aldehyde,
Yes. I will repeat the run 5 minutes after the 1strun is over. But that 2nd run is also at 40 degree celsius for 8 hours? Can you please clarify that?

Thanks

[Peter Apps]

It is not the analytical run that is at 40C for 8 hours. Both of the analytical runs (with no injections, not an injection of air) must use your usual temperature programme, gas flows etc. The 40C for 8 hours is with the GC in standby. So you put the GC on standby with the column at 40C and the carrier gas flowing and leave it for 8 hours. Then you do a blank run under your usual conditions but with no injection. Then you let the oven cool to the start temperature of your usual programme, then you immediately do another blank run with no injection under your usual conditions.

Peter

[juniorchem]

Ohh..I got it the wrong way.
I am using an auto sampler. So how do I run it without any injection? I ran a sequence without any vials in the sampler. Is that enough?Is that going to be a "no injection" run?

Sorry for asking these silly questions..

[AICMM]

Juniorchem,

Hitting the start button on the front of the GC should start a GC run without injections. As soon as the GC run is done and you are back to ready, do it again. You may want to go into Run Control and type in some informative information about this experiment so the files will be easy to find.

Best regards.

[juniorchem]

Thanks a lot for the explanation. That was really helpful.

I had mistaken this stand-by mode to be the analytical run for 8 hours at 40C. I am running the GC at 40C for the past 7 hours. How bad it is for the instrument?
Or can I just go ahead and start from the beginning?

[aldehyde]

As long as you have flow through the column its completely fine, and even with the flow off as long as it had helium going through it at some point its fine .

Starting the run without any injection at all is better, but making a blank injection with just the dry needle going in SHOULD be fine.

[tiggeria]

Do I need to keep the injector and detector on when the GC oven is kept at 40C for 8h or longer?
If yes, what temperature?