A Certificate of Analysis (COA) is the single most informative document attached to a research peptide. Read correctly, it tells you what the compound is, how pure it is, and whether an independent laboratory actually tested the batch in your hands. This is a field-by-field walkthrough of a real COA, and the red flag to watch for in each row.
A COA is a laboratory report, not a marketing sheet. Under quality frameworks such as ISO/IEC 17025 (the international standard for testing laboratory competence) and pharmacopeial method references like the USP and WHO guidance, a meaningful certificate ties a specific result to a specific batch, method, and date. If any of those anchors are missing, the document loses its evidentiary value, no matter how professional it looks.
Product name and sequence
The top of the certificate should name the compound and, for a peptide, state its amino-acid sequence in one-letter or three-letter code, along with the molecular formula and average molecular weight.
Red flag: a product name with no sequence, no formula, and no molecular weight. Without those, the identity result later in the document has nothing to be checked against.
Batch / Lot number
A COA describes one batch, not a product line. The lot number on the certificate must match the lot number printed on the vial or its label.
A COA is only valid for the exact lot it names. A certificate that carries no lot number, or a lot number that does not appear on the physical label, cannot be verified against the material you hold. Treat lot-specific certificates as the baseline, not a bonus.
Red flag: no lot number, a generic lot ("Batch: standard"), or a mismatch between paper and vial.
Manufacture and retest / expiry date
Two dates matter: when the batch was made, and the date by which it should be re-analyzed or is considered expired. For lyophilized peptides stored correctly, retest windows are common because stability is time- and temperature-dependent.
Red flag: no dates at all, or the same manufacture date appearing on certificates for many different lots (a sign the COA was recycled).
Appearance
A short physical description of the material, typically "white to off-white lyophilized powder." It is a low-tech but genuine check: your vial should look like what the certificate describes.
Red flag: a described appearance that clearly does not match the physical material, or a blank field.
Purity by HPLC
This is the number most people look for first. High-performance liquid chromatography (HPLC) separates the components of a sample; purity is reported as the percentage of total peak area attributable to the target peptide, usually with a specification of ≥98%.
A purity figure is only as trustworthy as the chromatogram behind it. The certificate should either embed or attach the HPLC chromatogram so you can see the main peak, its retention time, and any impurity peaks. A percentage with no chromatogram is an assertion, not evidence.
Red flag: a purity number with no attached chromatogram, no method named, or an implausibly perfect value such as "100.0%."
Identity by LC-MS
Purity tells you how much of the sample is one thing; it does not tell you what that thing is. Identity is confirmed by mass spectrometry, usually LC-MS, which measures the mass-to-charge ratio of the molecule. For a peptide, the certificate should report the observed mass against the expected value, commonly the protonated ion [M+H]⁺ or a multiply charged species.
HPLC and LC-MS answer different questions. A batch can be 99% pure and still be the wrong molecule. Only the mass confirmation ties the pure peak to the sequence named at the top of the page. A COA with purity but no mass is only half a certificate.
Red flag: no identity/mass section, or an observed mass that does not correspond to the stated formula.
Water content (Karl Fischer)
Lyophilized peptides retain residual water. Karl Fischer titration measures that water content as a percentage. It matters because reported peptide "content" and reconstitution behavior depend on how much of the vial's mass is water rather than peptide.
Red flag: the field is missing entirely, which is common on fabricated or oversimplified certificates.
Endotoxin (LAL)
The Limulus Amebocyte Lysate (LAL) assay detects bacterial endotoxin, reported in endotoxin units per milligram (EU/mg). It is a purity-of-a-different-kind measurement: not chemical identity, but microbial contamination.
Red flag: absence of any endotoxin result on a certificate that otherwise presents itself as complete.
Storage and handling
The certificate should state storage conditions consistent with the retest window, typically cold, dry, and dark. Storage guidance connects the stated stability to real-world handling.
The signature line: an accredited, named laboratory
Finally, look at who signed the document. A credible COA names the testing laboratory, references its accreditation (for example an ISO/IEC 17025 scope), and carries an analyst or quality-release signature. Independent third-party labs such as Janoshik are frequently cited in the research-peptide space precisely because the lab is not the seller.
Red flag: a certificate "issued" by the vendor itself with no independent lab named, and no accreditation reference or signature.