Explain how two different compounds with the same Rf value on one plate can be diff when cospotted?

Question

What I am trying to say is this: two different compounds are run separately using the same solvent system. Based on this they have exactly the same Rf value. However, when they are co-spotted and run together using the same solvent system, and observed under UV light, there are two separate spots, one higher than the other by a very small fraction. How is this possible? I don't need a full exaplanation- just some direction. I was thinking along the lines of functional groups but I'm not so sure how that would work.

Thanks in advance.

Answer 1

My experience is this:

Often compounds that are co-spotted can interact with each other and thus run differently, going with your functional group idea.

However, more often, I think it's just easier to tell really minute differences in Rf from cospotting. In separate lanes it can be difficult to tell if they run to the same level or not--depending on they're shape, degree of fluorescence, etc.