I have observed very strange behavior on the TOSOH Amide TSK80: by operating this column under HILIC conditions (5 mM AmFormate, pH =4.5/AcN as mobile phase) I have very good retention for synthetic peptides for only 5-6 injections. In later injections the analyte that was retained previously elutes already at void time! Nothing was changed between the injections and the detection is performed with both UV and ESI-MS. Any idea?