Acetone-d6 on purge and trap volatiles methods 8260/624/524

[acurtis89]

Hi all,

I'm analyzing volatiles per 8260/624/524 purge and trap/GCMS methods and having issues recovering the internal standard acetone-d6 on one of the instruments in our lab. If there ever is recovery, it is with an incredibly low response. The system has the following setup:

Autosampler: EST Centurion
Concentrator: EST Encon Evolution
GC/MS: HP Agilent 6890/5973

I've done a few things to troubleshoot/isolate the issue so far. I loaded vials that were manually spiked with the internal standard solution at 1uL/mL and programmed the autosampler not to inject IS. Acetone-d6 didn't show up in these runs, while the other internal standards had responses that aligned with samples injected normally by the autosampler. I also bypassed the autosampler completely by transferring 5mL of the exact same solution into the purge vessel and stepping to purge. This analysis again looked identical to a normal injection with IS added by the autosampler, with normal responses for all internal standards yet no response for acetone-d6. Finally, I performed a direct injection of the internal standard solution (2uL) onto the GC column. Acetone-d6 showed up and with a strong response relative to the other standards.

Based on these tests, it seems like it has to be getting lost somewhere in the concentrator. Leak checks pass and lighter compounds have a decent response, so it doesn't seem to be a leak. The concentrator was even refurbished last winter, yet the issue persisted. Without that internal standard we are limited to short list analyses on the system.

Please let me know if you have any suggestions on further isolating the issue, or if you have seen this before, and thank you!

[Steve Reimer]

What type of trap are you using and is your water management working as it should?
Has this system given good response for acetone before?
Is the response for unlabeled acetone ok?
Any other ketones in your analysis?
I don't have any experience with Encon concentrators but if my ketones go south I start by looking for where the water is collecting.

[acurtis89]

Traps: Teledyne "9" analytical trap, moisture traps are EST that I know of. They have been changed periodically with no difference in the results. The same traps work effectively for our other instruments.

It has shown up during my time in the lab (little over a year), while when it would it would be spotty/inconsistent. I'm told it used to run full list well.

Other ketones (unlabeled acetone, MEK, MIBK, 2-hexanone) look OK relative to acetone-d6, though relative to other compounds they are lower in response.

What other parts of water management could I look into? As far as the the P&T parameters, the dry purge flow is 60 mL/min for 1.5 minutes, which is as long or longer than similar systems.

[Steve Reimer]

On my OI concentrators I would check that the water management fitting are clean and heating properly, that the sparge tube didn't have accumulations at the top where it doesn't get rinsed and that the valve and transfer line heaters are heating properly. If all that was working I would change the trap (I use Vocarb traps and sometimes their heaters fail).
Someone familiar with Encons would be able to point you to their specific trouble points.

[acurtis89]

Thanks, I appreciate your input!