negative peaks HPLC

[Yata]

I have a problems with negative peaks. My systems is a gel permeation column with THF- methanol as solvent, I'm separating glicerol, triglicerides and ethyl esthers with an RI detector.

[tom jupille]

Can you be a bit more specific? Where do these peaks occur relative to your analytes? Are they always at the same retention times or do they move around?

[Kostas Petritis]

Generally speaking, if your samples contain compounds/solvents that have a refractive index lower than the refractive index of your mobile phase (i.e. TFA-methanol) then you will experience negative peaks when these compounds/solvents are eluted...