Peptide COA Verifier

01Identity — is this even the right compound?

The certificate header should state a molecular formula, a molecular weight and ideally a CAS registry number. All three are fixed properties of the substance and are published in public chemical databases. If the formula on the COA does not match the reference value for what you ordered, you are holding a certificate for a different chemical and nothing else on it matters.

One legitimate source of confusion: salt forms. Acetate and trifluoroacetate salts shift the molecular weight upward relative to the free peptide. A COA stating a salt form should say so explicitly. An unexplained mass offset should not be assumed to be a salt form.

02Purity — the chromatogram, not the number

A printed figure such as 99.2% is a claim. The evidence is the HPLC chromatogram behind it: a single dominant peak, a labelled retention time, and an integration table showing how the percentage was derived. What to look for beyond the headline number: shoulders on the main peak, which indicate a closely eluting related impurity, and unlabelled side peaks that never make it into the integration table.

A certificate that reports a purity percentage without showing the trace is asking to be taken on trust. That is precisely what a third-party certificate is supposed to make unnecessary.

03Mass confirmation — does MS agree with the formula?

Mass spectrometry confirms that the material is what the formula says it is. The observed mass must be consistent with the calculated molecular weight. One point trips people up constantly: peptides are usually detected as multiply charged ions, so the raw m/z value printed on the report reads considerably lower than the neutral molecular weight. A 4000 g/mol peptide might appear at m/z 1001 as the [M+4H]⁴⁺ ion. That is normal and not a discrepancy.

04Provenance — who issued it, and for which batch?

This is where most vendor COAs actually fail, and it has nothing to do with chemistry. A certificate carries authority because an identifiable laboratory issued it for an identifiable production run. It needs three things: the name of the testing laboratory, a batch or lot number that matches the label on your vial, and a date.

Peptide purity varies between synthesis runs, so a COA applies only to the batch it was issued for. Publishing a single representative certificate per product rather than per batch is common practice and substantially weaker than it appears. Checking that the lot number matches your vial is the most frequently skipped step in the entire process.

05The check almost nobody does — accreditation scope

A named laboratory is good. An accredited named laboratory looks better still. But an accreditation is never blanket approval: it certifies a laboratory for a defined list of methods, and that list is published. A lab can hold a genuine, current ISO/IEC 17025 accreditation whose scope does not include the test printed on your certificate.

We found exactly this while auditing a vendor in our directory. The laboratory is real, the accreditation is current, and the scope document lists nine microbiology assays plus three chemical method families: preservatives, trace elements by ICP-MS, and residual solvents. It contains no HPLC purity method and no peptide identity confirmation. The only mass spectrometry in scope is ICP-MS, which measures elements rather than confirming a peptide. The purity figure on that vendor's certificates therefore sits outside what the accreditation covers.

How to check it yourself: accreditation bodies publish scope documents. For US laboratories, search the A2LA public directory by laboratory name, open the scope PDF, and look for the actual technique, such as HPLC or LC-MS. If the method behind your number is not listed, the accreditation logo on the certificate is decoration rather than evidence.