iam eswa from oman we analyse cefixime product by hplc used short column (100*4.6*5) in that resolution is NLT 2.after 200 injections we cannot get it ,then theritical plate was also gradually decrease,in the mobile phase tetrabutylammnium hydroxide(

iam eswa from oman we analyse cefixime product by hplc used short column (100*4.6*5) in that resolution is NLT 2.after 200 injections we cannot get it ,then theritical plate was also gradually decrease,in the mobile phase tetrabutylammnium hydroxide(40%aqueous) after 200 injection required new column,how can overcome this problem