Peptide mapping is a useful method that can compare subtle differences between protein samples. The target protein is first digested by enzyme(s) to generate peptides. The peptide mixture will then be separated by HPLC under optimized conditions and detected by UV spectrometer. The obtained UV chromatograms contain signal intensities, which can be used to identify the peptides by online or offline MS detection and quantitative analysis. Once the HPLC-UV profile has been constructed, it can be used for batch comparison, lot-to-lot QC, sequence variant analysis, or comparative studies of biosimilar/reference drug.