What HPLC purity is considered good for research-grade peptides?

Purity by HPLC is the percentage of the target peak relative to all UV-absorbing peaks in the chromatogram. By common industry convention, research-grade peptides are expected at roughly ≥95–96% HPLC purity, with ≥99% considered excellent; the "missing" percentage is usually synthesis by-products such as truncated or deletion sequences. Two cautions. First, purity is only meaningful alongside an identity check (mass spectrometry) — a very pure peak of the wrong molecule is still wrong. Second, HPLC purity is not the same as net peptide content: a vial can read 99% pure yet contain less actual peptide than labeled once water, salts, and counter-ions (e.g., TFA) are accounted for. A strong COA reports purity, MS identity, and ideally net peptide content together.