How to convert/translate split inlet ratio new method

Discussions about GC and other "gas phase" separation techniques.

4 posts Page 1 of 1
My stuff:
FID GC: Agilent 6850
Software: Chemstation Rev B.04.02
Capillary column: 30 m x 0.25 mm x 0.25 um
Carrier gas: Hydrogen
FID gas: Helium

I am in the process of creating a new method based on a method meant for a 10 m x 0.10 mm x 0.10 um column and using Helium as a carrier gas. As stated above, I have a 30 m x 0.25 mm x 0.25 um column and I use hydrogen as a carrier gas. I have already used Agilent's method transfer program to convert/translate the majority of the method parameters. However, there is no place in the method transfer program to translate the split inlet ratio/ split flow/ total flow.

I know nothing about creating a method. Is there a formula or calculation I can use to figure out what my split inlet ratio or split flow should be?

Thank you so much for any insight!
I would suggest starting with your current split ratio, make an injection, and compare results. Column/inlet flows will be much different for that narrower column. My approach to optimizing my split ratio is to run my highest calibration point. If the chromatography suggests column overload (peak fronting), then I increase the split ratio. This puts less analyte mass on-column. Once the peak shape is acceptable, I run the lowest concentration calibration standard. If the responses are adequate for quantitation, I'm done. If the responses are more than adequate, I turn the split ratio up again.

1) Ensure split ratio is high enough that your high calibration standard doesn't overload.
2) Ensure split ratio is low enough for adequate response from your low calibration standard.
Regards,

Christian
cjm wrote:
I would suggest starting with your current split ratio, make an injection, and compare results. Column/inlet flows will be much different for that narrower column. My approach to optimizing my split ratio is to run my highest calibration point. If the chromatography suggests column overload (peak fronting), then I increase the split ratio. This puts less analyte mass on-column. Once the peak shape is acceptable, I run the lowest concentration calibration standard. If the responses are adequate for quantitation, I'm done. If the responses are more than adequate, I turn the split ratio up again.

1) Ensure split ratio is high enough that your high calibration standard doesn't overload.
2) Ensure split ratio is low enough for adequate response from your low calibration standard.


That is the best way to go about it. Just remember that with the 0.25 column your peaks won't be as sharp as with the 0.10 column so you may be going with a lower split ration to make up for a small loss in sensitivity, and the larger column can take a larger loading so you should not have to worry about overloading when using the settings for the smaller column.
The past is there to guide us into the future, not to dwell in.
Christian and James-

Thank you so much for your replies! As Christian suggested, I decided to pick an inlet ratio that allows my lowest calibration peak to still be picked up without having too high of a response from my highest peak. I spent much of the day yesterday working on it and I found a split ratio that works really well. As James suggested, my split ratio is quite a bit lower than the split ratio that worked with the 10 m x 0.10 mm x 0.10 um column.

My new method is now up and running. Thanks again for the help.
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