Reading an HPLC chromatogram

Reversed-phase HPLC separates peptides by hydrophobicity. The main peak is your product; everything else is either an impurity or an artefact of the method.

Four things decide whether a purity figure is comparable: the column and gradient, the detection wavelength, the integration threshold, and whether the sample was run as-is. A result quoted at 214 nm with a 0.1 % threshold is stricter than the same sample at 220 nm with a 1 % threshold, because small shoulders are counted in the first case and ignored in the second.

What to look for on a real chromatogram: a flat baseline, a main peak with no shoulder on the leading edge, and impurity peaks that are integrated rather than clipped by the threshold. A chromatogram that shows no impurities at all usually means the threshold is too high.