what is a good way to separate weakly absorbing compounds?

[dym]

It may be a naive question, but help me out guys!

[Uwe Neue]

Your question is not clear.
Do you mean "weakly absorbing" such as that you do not see them in the UV detector?
Or do you mean weakly adsorbing as they are not well retained on a reversed-phase column?

If you mean the latter, there are potentially several solutions, such as a C18 that can be used in 100% water, or HILIC, or ion-exchange.

Please describe your problem in a bit more detail!

[dym]

thanks
"weakly absorbing" means "weakly absorbing in UV range"

[tom jupille]

More nitpicking terminology here. The answer to your question is: "You separate them the same way you would separate UV absorbing compounds". The real issue is how to detect them!

The general choices (in order of increasing cost/complexity) are:
- refractive index (RI)
- evaporative light-scattering detectors (ELSD)
- mass spectrometry (LC-MS)

In addition, other techniques may work depending on the specifics of your analyte chemistry:
- conductivity detectior (if your analyte is ionized or ionizable)
- electrochemical detector (if you can easily oxidize or reduce your analyte at an electrode surface)
- post-column reaction detector (if you can react your analyte with something that will make it absorb UV or fluoresce)
- indirect UV detection (if you analyte can displace a UV-absorbing species in the mobile phase)

I'm probably missing some stuff here. If you can provide more details about what you're trying to do, people may be able to give more specific answsers.