Thermodesorption from Markes

[Absolutdude]

Hello,

I just startet to work with the Thermodesortption/GC-MS-System. I use the Markes Thermodesorber (Ultra Series2 + Unity Series2) coupled with a GC/MS.

I get more and more used working with the system and reading a lot in the Application Notes. But there are still some things I didn’t find out yet.

Where can I set the Flows at the Unity-Software (Column Flow, Desorb Flow, Split). Today I found out, that the box which says “Enter Flows” is just for calculation, not for actually setting the Flow.

I still have a lot of artefacts in the chromatograms. Even after heating the Trap and conditioning the tubes with high temperature.

Do you know about a TD-GC-MS method in a publication? I would like to check the system to see if I can measure as sensitive as I should.

Thanks for the Help,

Best regards

[Johnny Rod]

There are many application notes on Markes' web site, have a look and see if you can replicate one of them. Try speaking to Markes, they are generally quite helpful. We also see a fair number of artefact peaks from the tubes, less from the trap. I think they take a number of conditioning cycles to really clean up. Are your gases filtered/scrubbed?

[Absolutdude]

Thanks for the quick answer.

Yes I checked the artefacts with Blank-checks and they are also more from the Tubes as from the Trap.
I use stainless steel tubes (filled with Tenax).

How do you store your Tubes, if you don't use them?

[Johnny Rod]

They shodl be capped but we always condition them before using them. We don't use this equipment very much, so this is not a problem for us. You can also buy pre-conditioned tubes from Markes, I haven't tried them though.

[Spuzzin]

Hi,

If you don't have a mass flow controller then the flows are set using needle values on the unity. There is an option in the software to open the valves appropriately for setting the flows.

Artefacts are a part of TD. You have just have to prepare your tubes and traps appropriately and condition before use. Also selection of appropriate packing material helps.

Rich

[Absolutdude]

Hey Rich,

thanks for the answer.
I think I don't have a mass flow controller. So I think I have to go for the needle valves. I found two of them on the Unity ("Split" an "Trap desorp"). So this is for second desorption, right?

Where do I set the gas flow during Tube desorption and first Split ?

Where can I see the value of my flow? I can switch the needle valves, but still doesn't know how much the flow is.
(Yes I found the "set gas flow"-button)

Thanks again for the Help

[Spuzzin]

The flows are measured using a flow meter, the tubes are above needle valves .

The manual (available on the Markes website) details what the flows should be and where you should split, depending on what split ratio you want to achieve.

Rich

[MMJ88]

Hi Absolutdude,

I do similar work (though with a Gerstel system). Our software control (through Agilent Chemstation) is also quite confusing. I can't offer you any help on that, as I'm not familiar with the Markes system. I can however recommend some literature for you to check out. I have summarized a couple useful papers:

Junayapoon, et al. "Programmed Temperature Vaporization Injection (PTV) in the Analysis by Gas Chromatography-Mass Spectrometry (GC-MS) of the Constituents of Landfill Gas" - Tenax TD GC/MS method, like you requested.

Harper, Martin. "Sorbent trapping of volatile organic compounds from air" - Really nice review type paper on sorbents, TD, GC/MS. I found some useful bits in there for my stuff. Includes sections about Tenax. Has a good section on artifacts that can be formed from ozone or nitrogen oxides attacking the Tenax, could be relevant to you.

Borusiewicz and Zieba. "Comparison of the Effectiveness of Tenax TA and Carbotrap 300 in Concentration of Flammable Liquids Compounds" - Has good data on thermal desorption efficiency of Tenax TA. Relevant to your issues with conditioning and artifacts.

I have about 18 relevant (to some extent) papers I put into a little folder for myself to refer to. I can zip those up and email that to you if you find this stuff useful.

Best of luck!

[Absolutdude]

Hi MMJ88,

that sounds great.
I would love to read the papers and I am pretty sure theat they will help me with my the work.

How can I mail you my Mail-adress? Is there something like private Massages in the Forum. I did not find it yet...

[MMJ88]

Hey,
Email me at V1KQms6y8tot@meltmail.com (temporary email forwarding address, will expire in 24hr). I'll reply to that.

[AIM]

Can I please buy or barter for a copy of the Markes Unity 2 software? our computer crashed and I cant find the disk and Markes does not sell it anymore.

Alex