internal standards high for standards and low for samples

[chloesabrina]

I am running methods EPA 8260B by purge and trap on encon concentrators to a 6890N GC and 5973 MSD and I have a problem where my internal standards will rise with standards or any samples that have a large amount of analytes present in them. My blanks or cleaner samples will not pass the 50% recovery on the last internal standards which seems to be affected the most.
I have just cleaned the source and replaced the column because of this problem, but it did not improve. I run a ramped flow from 0.5ml/min which I increase to 0.8ml/min after 2 minutes. I have tried running a constant flow of 0.5 ml/min, but the problem was even worse.

Please send suggestions!!!

[carl.nott]

It sounds like you have a bad trap and/or actives sites in your purge-and-trap. The active sites are being 'filled' when you're running something with analytes present but when you're running clean samples they focus on your IS/SS.

I would...
Do injection port maintenance (replace liner and gold seal, if questions ask the semi-volatile folks for help, hehe).
Rinse line from GC transfer line connection point into weldment with methanol (blow out/let dry before re-attaching).
Replace concentrator -> GC transfer line.
Detach trap and transfer methanol from the autosampler (assuming you have one) to the purge vial on the concentrator to rinse the sample path (rinse 5-10 times with water afterwards).
Replace trap.

If this does not fix your problem you'll need to start tearing apart your concentrator and rinsing loops and valves (good times!).

Note that just replacing the trap will probably solve this issue but better safe than sorry, right?

[chloesabrina]

Alright, I have replaced the liner and gold seal and also rinsed transfer line from autosampler to concentrator with meoh and replaced soil needle. I am purging some standards and blanks to see how things look. I will let you know if this helps.

Thanks for the advice (used to work in svoa so I can do GC maintenance)

[JTM]

it's definitely a P&T issue, most likely a bad trap.

[chloesabrina]

I don't think that it is a bad trap because I run pt squared so the autosampler is hooked up to 2 concentrators and the odds of both traps being bad are minimal. I will change traps next though to eliminate that as a source of the problem.

[JTM]

both of them failing is fairly unlikely. can you temporarily bypass one?

[chloesabrina]

It's a tedious process, you have to disconnect the pt squared and then run your transfer line to the concentrator instead of the pt squared. It is worth a shot and if nothing else is working on Monday it will be my next step.

[carl.nott]

Well if it's pt^2 and effecting both concentrators I would definitely replace the heated transfer line from the concentrator(s) to the GC.

No offense meant with the injection port maintenance quip, I just found that when I bounced from voa to semi-voa (and back) voa folks tended to be less experienced with injection port maintenance and column replacement. On the flip side semi-voa folks tended to be more laid back when it came to turn-around time and making sure the instrument was able to run at any time.

[AICMM]

chloesabrina,

Change one of the traps, not both. Divide and conquer.

The other thing I would like to see is your split ratio. Since this is common to both traps I would look there first. In my opinion, it has to be something common to both systems since I agree with you about both traps being bad at the same time. My only caveat is that you did not last change both traps at the same time and from the same lot...

Best regards.