GC 8890 - Injected volume affects retention time

Question

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.

paulsalverda · Answer

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 In split, one reason the RTs move forward as more is injected is because of the higher instantaneous pressure in the inlet caused by the larger volume of solvent vapor created. It looks interesting here, but the difference from 0.3uL to 1.5uL is only 0.03 minutes at 4.45 minutes --- 1.8 seconds. 
 RT shift with different injection volumes is also related to a solvent effect &ndash; with larger injection volumes you&rsquo;re introducing a lot more solvent, which can start to have an effect on analyte solubility in the stationary phase and thus affect retention. Most customers don&rsquo;t see this because they stick with stable split and injection volumes (as they should), but retention behavior is a function of the whole method which includes how much solvent is introduced to the system. This is really only observable for peaks eluting in the neighborhood (relatively) of the solvent peak; real high boilers eluting at the end of the run will not show much impact due to their ability to cold trap and chromatograph much more slowly through the system, well after the solvent has been sent on its way.

GC 8890 - Injected volume affects retention time

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