The problem with fronting peaks can occur due to following reasons:
a) Interference in sample. Solution: Check column performance with standards. b) Shoulder or gradual baseline rise before a main peak may be another sample component. Solution: Increase efficiency or change selectivity of system to improve resolution. Try another column type if necessary. c) Column overloaded. Solution: Inject smaller volume or dilutions (e.g. 1:10 or 1:100) of sample. d) Sample solvent incompatible with mobile phase. Solution: Adjust solvent: Whenever possible, inject samples solved in mobile phase. Flush polar bonded phase column with 200 ml HPLC grade ethyl acetate, then with intermediate polarity solvent prior analyses.