Chromatography Forum

Hey, we are running on GC-FID-MS when we inject on our front injector we get a calibration curve which is fine and baseline is pretty clear but when we inject with the back injector we get alot of contamination and crap on our baseline. Just wondering what i should do? im thinking inject different volumnes and see if the contamination or what ever it is increase or decreases...if this is the case then it would suggest it is the injector....any other ideas what to do i would appreciate it?

If they're the same type of injector, it's pretty easy to just switch the columns over, and see if the contamination follows the column/detector or the injector. If thats what you've done (its a little hard to tell your configuration from your description) then you could have already determined that the inlet is full of rubbish...

couldnt swap them around...some sort of communication error when i did

What kind of GC and data system are you using? This sounds like an issue with setting up software (at least on the systems I know).

Hey Don...you mean in relation to swapping the detectors?....really thats not the problem. i just swApped them back and they work fine. Im using Agilent CDS GC-FID-MS

I was following the reply to Peter B and it looked like there was a communications problem after trying to switch the columns between inlets to see if the junk was indeed in the inlet. I may have misunderstood what was the cause of the communictions problem.

Depending on the usage of the inlets ( has the "cruddy" one seen more injections than the clean one) it maybe time to clean. Have you tried changing the linet and gold seal with a column cut?
Don't forgrt the split vent line and trap.
Have you done a no injection run to see if it's the column?

Are you talking injector such as a 7683 or the injection port? If injector have you tried a new syringe?

I wasn't suggesting anything to do with the electronics, I simply meant to undo the two column nuts and swap the columns over (so the column that was plugged into the front is now plugged into the back (and vice versa). The only very modern GCs I use are Agilents, but I can't think of any GCs that wouldn't let you do this without affecting the communications at all (unless of course you have two different styles of inlets installed with different column fittings.)

If you have contamination (or other abnormal symptoms) in your system in one channel (in a dual channel system), but not it the other, you can often narrow down its source by changing the inlet ends of the columns over. If the contamination stays on the same channel, it's in the column or the detector. If it changes channels, it's in the inlet, carrier gas line or in what you're injecting...