The chromatogram of cefixime in lc ms ms is tailing

i am running cefixime in human plasma with hplc tandem with tqd. it's appears the chromatogram is always tailing. Can somebody tell me what to do.
by the way i am using phenomenex c18 column 100 mm with porousity 5 um. Solvent is acetonitrile and formic acid 0.125%.
Thank you