The Cogent Bidentate C18™ phase can be stored in un-buffered aqueous / organic solvents, but flowing significant bed volumes of un-buffered aqueous will cause a drop in efficiency of approximately 35% before reaching a new steady state. This is why we recommend either acid or basic buffers but not un-buffered eluents during analysis.
For storage 0.04% v/v phosphoric acid ( 85% bench phosphoric acid ) is preferred.
No, Phosphoric Acid will not precipitate in the columns.
Sodium phosphate (which is not recommended) but which is often used as a buffer, will precipitate in the columns and should be avoided as a storage solvent for all HPLC Columns.
Phosphoric acid may be used to acidify 99+ % organic solvents such as methanol and acetonitrile without precipitation provided no sodium salt used.