When you order a research peptide, you are not just buying a compound — you are buying a claim. The claim is that the vial contains what the label says, at the stated purity, free from harmful contaminants. Documentation is the only mechanism by which that claim can be independently evaluated. Without it, you are operating entirely on trust.
What is a Certificate of Analysis?
A Certificate of Analysis (CoA) is a formal document issued alongside a specific batch of a product that records the results of quality testing performed on that batch. It is not a general product specification sheet — it is batch-specific. A CoA for BPC-157 Lot #001 tells you about that particular lot of material. It tells you nothing about Lot #002, which may have been produced under different conditions, from different starting materials, or at a different site.
This distinction is critical for research reproducibility. If you are running experiments across multiple batches, the consistency of documentation across those batches is as important as the documentation itself. A supplier who provides batch-specific CoAs for every lot enables reproducible research. A supplier who provides a single generic document for all stock of a compound does not.
What a complete CoA must contain
Purity vs identity: two different measurements
A CoA that contains only a purity percentage is incomplete from a quality assurance standpoint. Purity (measured by HPLC) tells you what proportion of the sample is a given compound eluting at a given retention time. It does not confirm which compound that is. Identity confirmation, typically via mass spectrometry, tells you whether the compound is actually what it is claimed to be by measuring its molecular weight and comparing to the theoretical value.
The failure mode is real: a sample could be 99% pure by HPLC — with a large, clean main peak — but if the compound is the wrong peptide (perhaps a synthesis error producing a related sequence), purity-only documentation will not detect this. Identity confirmation is not an optional extra. It is a necessary component of complete quality documentation.
Red flags in supplier documentation
The following should be treated as meaningful warning signs when evaluating a supplier's CoA: no batch or lot number; identical purity figures across every product they sell (e.g. every compound is exactly 98.5%); no testing date; no contact information for the issuing party; purity stated without an analytical method; documents that appear to be templates with no batch-specific data; and suppliers who cannot tell you which batch of stock is currently being dispatched. These are not minor omissions. Each indicates either that genuine analytical testing was not performed, or that the documentation provided does not correspond to the actual product being sold.
Understanding the issuer of a CoA
A CoA is only as reliable as the party who issued it. A supplier who issues their own CoA is effectively self-certifying quality — analogous to marking one's own exam. The value of a CoA is substantially higher when issued by a party that is independent of the supplier: an analytical laboratory with no commercial interest in the result. When evaluating supplier documentation, note who issued the CoA and their relationship to the supplier. Third-party documentation from an independent analytical laboratory represents a meaningfully higher standard of assurance than in-house supplier documentation.
Questions to ask before every purchase
Before placing an order with any peptide supplier: Can you provide a batch-specific CoA for the stock currently being dispatched? What analytical method was used to determine purity? Is identity confirmed separately from purity, and by what method? What is the batch number for current stock? A supplier who cannot or will not answer these questions should not receive your research budget.