Peptide purity vs peptide content: what does a COA tell you?
When reviewing research peptides in the UK, distinguish chromatographic purity, net peptide content and measured quantity. These results answer different questions.
Chromatographic purity
A UV-HPLC purity result describes the target peak relative to the integrated, detected peaks under the reported conditions. A figure such as 99% is not, by itself, a measurement of milligrams in a vial.
Net peptide content
Lyophilised material may include moisture, counterions and residual solvents. Net peptide content assesses the peptide fraction relative to non-peptidic material; it can include peptide-related impurities. It is therefore distinct from target-peptide purity.
Measured quantity
A quantity result requires an appropriate quantitative method and a stated reporting basis. Check whether a value refers to gross material, peptide content or the target compound, and review units, sample identification and method notes. Do not calculate verified milligrams from a purity percentage alone.
For example, a product labelled 10 mg with a 99% HPLC result does not automatically establish 9.9 mg of target peptide. That conclusion needs quantitative evidence and the correct reporting basis.
Before relying on a report
- Match the report to the sample and supplied material.
- Identify which tests were performed and what each result means.
- Request missing quantitative information when your experiment depends on it.
Use the available certificates of analysis alongside the specifications for GHK-Cu 100 mg or KLOW80 research blend. This guide does not establish the purity or quantity of those products. For blends, check each component rather than assuming one percentage quantifies them all.
References: Bachem: quality control and net peptide content; Bachem: purity, assay and absolute peptide weight. Laboratory research only; not for human or veterinary use.
Sources and further reading
- Hoofnagle et al. (2016): recommendations for peptide standards, quantification, storage and handling for mass spectrometry.
- Agilent: peptide standards and analytical characterisation.
- Hureau et al. (2011): X-ray and solution structures of copper complexes of GHK and DAHK, DOI: 10.1002/chem.201100751.
Editorial review: 11 October 2026. This information supports critical reading of laboratory documentation; it does not certify a product or replace method validation.