We have recently attempted to adapt an HPLC method for the separation of algal pigments to an Agilent rapid resolution HPLC, which is configured with a microdegasser and a binary pump, both of which can handle the high pressure resulting from the rapid resolution capability. We tried adapting our mobile phase which is 30% 28mM aqueous TBAA and 70% methanol. Our solvent B is straight methanol. We run a gradient method on a C8 silica column. We have found that after running this mobile phase over time ( a matter of days) the backpressure on the column becomes unstable, slowly and infinitely increasing over time. The chromatography is, however, sufficient. When using a Quaternary pump and regular degasser, we do not see this pressure instability. I am starting to wonder if the TBAA mobile phase is affected by the high pressure, that maybe a salt precipitates out and builds on the column. When a fresh column is placed inline, the pressure starts off low (120 bar) and builds over time (270 bar or higher). Agilent has tested the columns and not seen particulate matter on the inlet frit but they do note the higher pressure of the column. I am wondering if something is precipitating out under higher pressure and accumulating on the silica. Any thoughts on TBAA or ammonium acetate chemistry under higher pressure? Or any good chemistry resources? Thanks! 8)