Peptide purity percentages on a Certificate of Analysis (COA) indicate how much of the analyzed material corresponds to the target peptide relative to detectable impurities under the stated test conditions, usually by HPLC. A result such as 95% purity does not mean the peptide is 95% chemically identical in every sense; it means the main chromatographic peak represents most of the sample, with the remainder attributed to related compounds, truncated sequences, salts, or other impurities.
How to interpret the value
- Method matters: Purity depends on the HPLC column, mobile phase, gradient, and detection wavelength used.
- Different assays may differ: A COA may report purity by HPLC while identity is confirmed separately by mass spectrometry.
- Compare like with like: Purity percentages are only meaningful when the same analytical method and reporting basis are used.
For laboratory purchasing, review the full COA, including test method, batch number, and acceptance criteria. Research peptides are intended for research use only and are not intended for human consumption.