interaction between C18 stationary phase with HPMC and PVP?

[NCCHEMGEEK]

Could this situation be an interaction between stationary phase and excipient?
I’m currently running 6 formulations that contain combinations of HPMC-AS and PVP-VA64 (or Kollidon VA64). I’m currently using an Agilent Infinitylab Poroshell 120 Bonus RP (P/N 695968-901) column (4.6 x 100mm; 2.7um particle size).
I noticed that the retention time of the NCE in my standards have shifted after I ran my 6 formulations. Can the combination of HPMC-AS, and or Kollidon VA64 being deposited on the head of my LC column be causing the retention time of my active to shift? Note, I am not using a pre-column.

[Perreman]

I know that PVP in Ph.Eur. specifies that the guard column must be backflushed after each injection. I've also experienced issues with running PVP in other sample types. So yes, PVP is possibly clogging/coating the head of your column which could change retention times.