Injection volume as a function of stationary phase

[adam]

Has anyone else noticed that the volume you can inject seems to decrease with the polarity of the phase.

In other words, we find we can inject less on a phenyl column vs a regular C18 column.

Has anyone else found this to be the case.

[Uwe Neue]

What is the injection solvent? If different from the mobile phase, this is a question of enrichment of the analytes. Otherwise, I would expect a roughly 2-fold difference in loadability between a C18 and a phenyl ligand of equal surface coverage on the same particle, but most people won't see that unless they do true preparative chromatography.

[adam]

We've tried different solvents. With Acetonitrile we see more of a difference than with something like methanol: but in all cases we are able to inject more on C18 than phenyl.

I don't think it's a mass overload issue though. We see the same type of peak distortion for smaller peaks. I believe that it is a volume overload issue (basically there seems to be more focusing at the head of the column with the C18 phase).

[AdrianF]

Ideally your injection solvent should be equal to or of weaker eluting power than the mobile phase. If you use pure solvents there is bound to be distortion except for very small volumes. (10ul or less)

[Uwe Neue]

This is less of a volume overload situation but a case of a bad choice of the sample solvent. In this case it could very well be that a packing that is more retentive will suffer less from this problem.