I’ll admit, I’m more well versed in liquid chromatography, but I think I’ve dabbled enough in GC to get your wheels turning.
There are a few variables you can start with:
- injection volume
- Carrier gas type
- Carrier gas flow rate
- Column type - I’m not sure what your column is made of, but Restek makes a reliable fused silica column for RS. Obviously if your analytes are not attracted to the stationary phase, you won’t get separation
- Oven temperature/ramp rate
Here is a good link from Restek showing great separation between pentane and acetone:
https://www.restek.com/pdfs/solventsincannabis_csc-poster.pdf
Check it out and let me know if you are still having trouble. I have a hunch it’s going to come down to your oven parameters. Maybe try something along the lines of what Restek has, I think starting at 140C is a bit hot for the volatile compounds.