How to read a certificate of analysis

A purity percentage on a COA is a measure of the target peptide against the total measured signal. It usually comes from HPLC peak area. For now, read it as a sign of how pure a sample is. It does not, by itself, prove identity. That is why identity checks by mass spectrometry matter alongside purity. HPLC is a method that sorts the parts of a sample. Mass spectrometry is a method that measures the weight of molecules.

A certificate of analysis is a document made by an analytical laboratory. It reports the identity and purity of a batch of material. For a research peptide, the COA should link the batch you hold to a set of measured results. These results are usually produced by third-party laboratory analysis.

The certificate only means something when it refers to a specific batch. Purity results from one batch do not guarantee the same results for another batch of the same product. So the batch number on the certificate should match the batch number printed on the vial you received.

The first section of a COA names the material under test. It should list the product name and the compound it is reported to be. It should also show the molecular formula and often the molecular weight. Check that these match what you ordered and what is on the vial label.

Identity checks are not the same as purity measurement. Identity tells you which compound the results relate to. Purity tells you how much of the sample is that compound, rather than other material.

The batch or lot number ties the certificate to a specific production run. Always compare the batch number on the COA with the one on the vial label. They must match for the certificate to apply to your material.

The certificate also usually carries a testing date or issue date. This tells you when the analysis was done. It helps you judge how current the certificate is against when the material was supplied.

The purity percentage is the headline figure on most certificates. It reports how much of the sample is the target peptide, usually as a percentage. Purity values for research-grade peptides vary by supplier and product. The certificate should state the figure reached through the method used.

Reading the purity figure on its own can mislead. So look at it alongside the methods section to see how the number was made. A stated purity is only as reliable as the technique used to measure it.

Most certificates measure purity with high-performance liquid chromatography (HPLC). HPLC separates the parts of a sample and measures the area under each peak. A high-purity material shows one dominant peak.

Mass spectrometry confirms the identity and molecular weight of the compound. It checks that the measured mass matches the expected mass for the peptide. Many certificates combine the two. They use HPLC for purity and mass spectrometry for identity. The COA should state which instruments and conditions were used, so the results can be repeated.

Reading the methods section takes some practice. But a few markers are worth looking for. A stated retention time, a column type and a flow rate suggest a real HPLC run, not a generic figure. A measured molecular weight close to the theoretical value, within an acceptable tolerance, supports the identity claim.

Alongside purity and identity, many certificates test for contaminants. Endotoxin testing measures bacterial endotoxin, usually reported in endotoxin units per milligram. It is a routine check for material handled in a laboratory environment.

Heavy metals testing reports the levels of elements such as lead, mercury and cadmium, usually in parts per million. These results show whether the material falls within the supplier's limits for leftover contamination.

Some certificates also list active ingredients or peptide content as a percentage or a concentration, next to the relevant limit. Where a limit is given, check whether the measured value sits within it. A result should normally be at or below the stated limit, not just close to it.

Verification starts with the obvious checks. Does the certificate name the right product? Does the batch number match the vial? Are the results dated? Then check that the methods are ones you know and that fit peptides, such as HPLC and mass spectrometry. Also check that the results are consistent with each other.

Where a supplier makes a certificate available, it should be specific to the batch you received, not a generic document. If you have questions about a batch, many suppliers publish a lookup tool, such as the certificate of analysis status page. That page lets you confirm what documentation is available for a given product or batch. As a working example, a product such as the GHK-Cu 50 mg vial would be supplied with its batch-specific certificate documentation for review.

Keep the certificate with the material it describes, in paper or electronic form. That way the batch record is complete if you need it later for an audit or a question. Storing the certificate with the laboratory notebook page for that batch makes the link easy to trace. Related guidance is available in the article on what HPLC and mass spectrometry prove and the article on choosing a peptide supplier.

For primary literature, search PubMed for HPLC peptide analysis. For compound records, browse PubChem. Use the certificate of analysis status page to check what documentation is available for a batch.

All products referenced in this article are supplied strictly for laboratory research use only. They are not medicines, are not licensed or approved for human or veterinary consumption, and must not be administered to humans or animals. Nothing in this article is medical advice. Researchers are responsible for operating within their own institution's and jurisdiction's applicable regulations.