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Thread: Static charge and isotope ratio's on GC-MS measurements

  1. #1 Static charge and isotope ratio's on GC-MS measurements 
    Forum Professor Zwolver's Avatar
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    A bit of background.

    I have a GC-MS connected to a metal chamber (0.001Atm), controlled environment, mostly containing regular isotope ratio CO2, and some other gasses like watervapor and N2 inside.

    If i measure at different humidities on the outside of the chamber, i will get different isotope ratio's measuring from he GC-MS. different humidity, different amount of heavy CO2.

    I guess it is something like a static charge on either the chamber or on the GC-MS. Or the tubing it is connected to eachother with. (grounding everything is impossible)

    The question is, why is this?

    22% 21,4C Humidity Shows 30%+/-2% different isotope ratio's for both CO2, and H2O, than 43% 21,1C Humidity. (have to check if it was higher or lower, but it shouldn't matter as it should show the same results)

    Is it the chamber, is it the gas from the system, is it the GC-MS itself, or is it a combination. We tried to have the same conditions, same gas, humidity inside the chamber is the same, etc.

    Hope any of you have more experience using a GC-MS so you can tell me it usually doesn't do this.


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    Bullshit Intolerant PhDemon's Avatar
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    What temperature are your GC column and detector? If they are too low it could be differing amounts of condensation affecting your results. Try increasing the column temperature and detector temperature to above 100 C and see if this fixes the problem.


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    Forum Professor Zwolver's Avatar
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    Quote Originally Posted by PhDemon View Post
    What temperature are your GC column and detector? If they are too low it could be differing amounts of condensation affecting your results. Try increasing the column temperature and detector temperature to above 100 C and see if this fixes the problem.
    Thanks, but that isn't how this GC-MS works as far as i know. It uses a GC column injection system, merely to guide the gasses through the MS in a constant rate (not overloading it). I can't find a temperature indicator on the GC-MS part anywhere. It even doesn't use a carrier gas. Merely High vacuum area's.

    The university calls it a GC-MS, but it is more like a Gas-MS. It is custom made, and specifically for elements/compounds like N2/NO/CO/CO2 and very small/light gaseous substances.

    So, only a GC in name, not function. It is basically one of these connected to a GC port, and not even containing a column, just the injection mechanism.

    Sorry i can't be more clear, but it's a problem people usually come to me with on a whim. A postdoc couldn't figure out a reason. I proposed it had to be static charge, but i didn't understand the process of how isotopes from elements would be drawn into the device from the chamber more frequent than others. This would basically destroy the whole function of the setup, or would prove a whole different idea.
    Growing up, i marveled at star-trek's science, and ignored the perfect society. Now, i try to ignore their science, and marvel at the society.

    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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    Bullshit Intolerant PhDemon's Avatar
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    OK, never used one of those before... It could be water vapour somehow interacting with the ions formed in the MS, is there any way you can dry the gas before it enters the MS? A small inline trap containing a drying agent would do the job.
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  6. #5  
    Forum Professor Zwolver's Avatar
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    Quote Originally Posted by PhDemon View Post
    OK, never used one of those before... It could be water vapour somehow interacting with the ions formed in the MS, is there any way you can dry the gas before it enters the MS? A small inline trap containing a drying agent would do the job.
    The pressure inside the precolumn is below 1*10^-5 atm.. I believe drying agents wouldn't work. Plus, we want to measure the watervapor too, it is an important part of the study.

    Only option would be to put the setup in a climate chamber. But our "climate" chambers are not controlled for moisture . Officially it is, but if you put it below 10C it will rain within a week.
    Growing up, i marveled at star-trek's science, and ignored the perfect society. Now, i try to ignore their science, and marvel at the society.

    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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    Bullshit Intolerant PhDemon's Avatar
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    Sorry then, I'm out of ideas...
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