Isolation of peaks from solvent front for GC/FID

[semivoadude]

Does anyone know why peaks sometime elute with the solvent front? I use a GC/FID 5890 and Mecl2 as a solvent. I run an aliphatic hydrocarbon standard and sometimes see C8 and/or C9 elute with the solvent front. Other times there is no problem, (peaks C8, C9, etc.. are isolated from the solvent front.
I use the same temperature ramp and pressure settings each time. Why do I get isolation only sometimes? what measures can be taken to prevent this?

Thanks!

[chromatographer1]

The only reason that comes to mind quickly is the amount of solvent you are injecting. If you widen your solvent peak from a too large sample or poor injection technique it can mask the peaks you mention.

[Mark]

As chromatographer1 implied this should all be a function of the injection, either a nonoptimized technique (must get in fast-inject fast-get out fast) or if you are removing the column to change liners or clip a small portion off the inlet of the column the positioning of the column in the injector is critical, a millimeter difference can be the difference between good sharp peaks or wider non-ideal peaks. Also in this vein, if you do not get a good square break when you cleave a portion off the inlet of the column this will cause problems also. Just some random thoughts on the problem.

Regards,
Mark

[varian]

Your column flow is to high or your start temp is high.
Reduce flow or reduce start temp. Longer column works too.