Separation of two peaks with the same retention times

[josephip]

I am currently trying to seperate two chromographic peaks which have the same retention times. I use two mobile phases with 95% and 90% methanol. Does anyone have any tips?

[tom jupille]

You're not giving us a whole lot to go on here.
What do you know about the molecules (how do they differ)?
What k' are you getting with 90‰ MeOH?
What column?
What temperature?
What pH?
What else have you tried?

[aldehyde]

spectral analysis with a DAD or two columns. Or change your method conditions, either way we need way more info about your equipment and sample.

[Gerhard Kratz]

If one of your compounds is neutral and the other charged you can try HILIC columns to get a baseline separation. Are both neutral but have large difference in MW SEC can be tried.
Anyhow, more information is needed to help you more.