Dear Wadim,

Thank you very much for your quick reply. I will try  with silica emitters and compare with metallic at higher pH

Not much difference experimentally. The use of "bioinert" materials for phosphopeptide analysis is grossly overhyped. Yes, steel emitters theoretically bind phosphopeptides; in practive, however, the surfaces are "saturated" after a few abundant digest injections onto your LC/MS. The most you will see is a slight increase of Fe-adducts if you look very closely. I would still encourage you to try this out on your home system if you can using a standard sample.

Thank you very much Christof!, I was told by a colleague who an orbitrap that he observes no significant difference in the level of phosphopeptide detection, it might be due to the fact they are analysing phosphopeptide-enriched samples on a regular basis and they saturated the steel emitter