Chromatography Forum

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!

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.

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

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