Reading a certificate of analysis

A certificate of analysis is the only document standing between a buyer and an unlabelled vial. It is also routinely misread. Most of the confusion comes down to one distinction that certificates rarely make explicit, and that almost no vendor explains.

Purity is not content

An HPLC purity figure answers a narrow question: of the peptide-related material detected in this sample, what fraction was the intended peptide? A result of 99% means the chromatogram was dominated by one peak and the remaining 1% was split among impurities and truncated sequences.

It does not answer the question buyers think it answers, which is how much peptide is in the vial. That is a separate, quantitative measurement — typically amino acid analysis, quantitative NMR, or a mass-balance calculation accounting for residual water, counter-ions and salts. A vial can be 99% pure and contain substantially less peptide than the label states. The two figures are independent, and a certificate showing only the first tells you nothing about the second.

The practical consequence: purity says the material is what it claims to be. Content says how much of it there is. Most certificates report only purity.

What to check, in order

1. Does the lot number on the certificate match the vial?

A certificate is a statement about one specific batch. A certificate for lot A tells you nothing about lot B from the same seller. If the lot number is absent, illegible, or does not match the vial in hand, the document is decorative.

2. Who ran the test, and is the report theirs?

Third-party certificates carry the testing laboratory's own letterhead, contact details and a report identifier that the lab can confirm. Several laboratories serving this market publish a verification lookup, so a report identifier can be checked against the lab's own records rather than taken on trust. A PDF bearing only the seller's branding is an in-house claim, not an independent one.

3. Is the date plausible for the lot?

Certificates dated long before or long after the batch they describe are worth questioning, as are certificates reused across multiple lots.

4. Which assays were actually run?

Look for what is present, then for what is absent. A typical certificate reports appearance, identity by mass spectrometry, and purity by HPLC. Frequently absent: quantitative content, water content by Karl Fischer, residual solvents, counter-ion identity and quantity, endotoxin, and bioburden. Absence is not evidence of a problem — but it is the boundary of what the document actually establishes.

5. Does the mass spectrometry result match the expected mass?

Identity confirmation compares an observed mass against the theoretical molecular weight of the target sequence. Our compound records list the verified molecular weight where we could confirm it against a primary chemical database, which makes that comparison possible without trusting the certificate's own arithmetic.

What a certificate cannot tell you

It cannot tell you the material was handled correctly after testing. Cold-chain excursions, repeated freeze-thaw cycles and light exposure all occur after the sample leaves the laboratory. It cannot tell you that the vial you received came from the tested batch. And it cannot establish sterility, pyrogen status, or fitness for any use in humans — assays of that kind are not what these certificates are.

Reading the numbers honestly

Two figures on the same certificate can appear to conflict without either being wrong. A high purity figure alongside a lower content figure is the expected result for a lyophilized peptide carrying residual water and trifluoroacetate counter-ions — that mass is real, it is in the vial, and it is not peptide. Certificates that report only purity leave this invisible, which is why a 99% figure so often reads as a stronger guarantee than it is.