Chromatographic studies of unusual on-column degradation of cefaclor observed in the impurity separation by HPLC.

•Unusual on-column degradation caused a ghost peak in the HPLC analysis of cefaclor.•The ghost peak was an oxidative decarboxylation degradant of cefaclor resulted from elevated column temperature.•The mechanism of on-column oxidative decarboxylation of cefaclor and several prevention measures were proposed.