I am conducting a HPLC analysis, omeprazole in mobile phase: phosphate buffer pH8 (0,05M): ACN (75:25); detector UV 302nm, column Zobax C18, module: Agilent 1100.
The trouble is that the base line tends to increase (about 0,3mAU per 10min). I have replaced the old precolumn but there isn't any improvement. My column is not too old.
Plz tell me all the possible reasons and the solutions. Thank you.