Hello Zohre,

You are right - using a small membrane will let small phosphopeptides elute through along with the Fe.

Perhaps a better approach would be to chelate the phosphopeptides with titanium dioxide beads, then wash away the Fe (and other minerals). You will then have phosphopeptides attached to the beads which you can elute with high pH, giving you demineralised phosphopeptides.

Kind regards,

Peter

Hello Mr Allen Faul,

Thanks for your valuable response.

I performed Tricine-SDS-PAGE for my samples (total peptide solution before the ultrafiltration and its permeate and retentate after the ultrafiltration), but the result was not in accordance with my idea!

There was no detectable band for the permeate, and the bands of retentate and the total protein were similar to each other.

Can we say that it is due to likely linear (not globular) conformation of low molecular peptides that might prevent them to pass through the membrane?

Thank you in advance for your consideration,

Zohre Delshadian