1,2,4-trimethylbenzene breakdown?

[jmacdonald1990]

Hi guys,

This is my first post on here so apologies if I break any etiquette. I'm a relatively new VPH/GRO GC/FID-PID analyst and I'm having an issue that seems to be stumping a lot of the more experienced analysts at my job.

I started seeing breakdown of 1,2,4-trimethylbenzene recently after a coworker tried to use a water instrument to run a soil curve (the instrument had not used the soil sample pathway in years, if ever). The response for all other analytes is pretty much stable, while this one compound is dropping between 25-35% in response, while simultaneously new peaks are appearing later in my run (some before naphthalene, some after naphthalene, all after 124-tmb). Tech support recommended purging 5ml of MeOH for 90 mins and then replace the traps. This solved it for a week or so, but now I am seeing the issue pop up again. The peaks are showing up on both the FID and PID. I've tried searching online for anyone who has had similar issues with this compound and I've found nothing useful.

Has anyone seen breakdown of this compound before? As someone who is new to the world of GC instrumentation, it's tough for me to know where to start. What kind of issues typically cause breakdown like this? Is it likely a foreign substance stuck on the instrument somewhere? Or is it more likely some kind of activation site or "cold spot" or something else entirely? Any guidance on where to start, and any other details that are needed I am more than happy to supply.

[rb6banjo]

Welcome to the forum. This material - like it's cousins (other alkyl benzenes) should be very inert chemically. I can't come up with a scenario in a GC sampling system where it would react to form something else.

Please provide as much detail as you can about your mode of sampling and your GC conditions. The rule of thumb on this forum is "the more information you can provide, the better will be the suggestions you get back".

[James_Ball]

As above we need to know the model of purge and trap system, what trap you are using, temperatures, ect.

1,2,4-tmb should not break down, and if it was breakdown the breakdown products should elute earlier than the parent compound. Usually if you are losing something like this, it is adsorbing somewhere in the system due to contamination.

Also what type of transfer lines are you using? (silcosteel, nickel, fused silica)