GC 8890 - Injected volume affects retention time

Hello everyone, I am working on GC/MS (8890 GC-5977B MSD). I run Methanol (in CS2) by DB-WAX column but the retention time of MeOH seem to be changed when I adjusted the injected volume 0,1; 0,2; 0,5; 1; 5 µL(other parameters still the same). Can somebody explain that phenomenon? Thank you for your help.

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  • Seems like you evaporate your methanol into a volume that is far bigger than your liner volume (Consider CS2 volume plus methanol volume). This is called overloading, you see that the end of your peak stays the same, that's also typical for overloading. You still have not so much, that the typical fronting can be seen. You can find some general information about overloading here: Help! My Peaks Look Strange - Fronting and Tailing in GC - Wiki - Consumables - Agilent Community

    Other peaks can be influenced because your methanol vapour plug changes the mass transfer between phase and carrier gas vs. phase and carrier gas+methanol plug.

    As a second comment: CS2 is highly apolar and you use a polar phase, this also affects the mass transfer.

    But still Paul is right you only see a retention time shift of 0.1 min max (6 secs), which is not critical.

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  • Seems like you evaporate your methanol into a volume that is far bigger than your liner volume (Consider CS2 volume plus methanol volume). This is called overloading, you see that the end of your peak stays the same, that's also typical for overloading. You still have not so much, that the typical fronting can be seen. You can find some general information about overloading here: Help! My Peaks Look Strange - Fronting and Tailing in GC - Wiki - Consumables - Agilent Community

    Other peaks can be influenced because your methanol vapour plug changes the mass transfer between phase and carrier gas vs. phase and carrier gas+methanol plug.

    As a second comment: CS2 is highly apolar and you use a polar phase, this also affects the mass transfer.

    But still Paul is right you only see a retention time shift of 0.1 min max (6 secs), which is not critical.

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