12 min read · updated 2026-10-20
How to Read a Peptide Certificate of Analysis
Line by line, using a real published lot: what purity, identity, quantity and endotoxin results mean, and the certificate errors worth catching.
Start with the lot number
A certificate describes one batch. Before reading any figure, confirm the lot number on the certificate matches the lot number on the label. A certificate for a different batch tells you what a different batch measured. On nearly all the lots we publish, the code ends in the month and year of manufacture, so lot BPC10VBG0326 was made in March 2026. That gives a quick cross-check: if a code’s suffix and the stated manufacture date disagree, ask the supplier which one is right.
A worked example: BPC-157 lot BPC10VBG0326
Here is how the published results for one real lot read, line by line. Lot and dates: BPC10VBG0326, received by AxisPharm, LLC on 2026-03-25 and reported 2026-03-25, manufactured 2026-03, best before 2028-03. The report date is on or after the received date, as it must be. Purity: >99.5% by HPLC-UV (208 nm). The ">" means the laboratory is reporting a threshold the main peak cleared, not an exact figure. Identity: 1421.1 [M+H] by LC-MS (ESI+). The molecular weight is 1419.5 g/mol; adding one proton gives an expected [M+H] of about 1420.5, and the measured 1421.1 sits within the tolerance of routine LC-MS. Identity is confirmed. Quantity: label claim 10 mg, measured 10.1 mg. The tested material meets its label claim. Endotoxin: 0.057 EU/mg by LAL assay.
Purity: what the HPLC figure tells you
Purity by HPLC is the share of the detected peptide signal that belongs to the target sequence rather than truncated or modified versions of it. It is calculated as an area percentage of the chromatogram peaks. Detection wavelength matters: low-UV detection around 205 to 220 nm sees the peptide bond itself, so it works for any sequence, while 280 nm relies on aromatic residues and can misreport sequences that lack them. Purity describes the peptide material only. It does not tell you how much material is in the vial; that is the quantity line. The chromatogram behind the figure is part of the laboratory’s certificate, and you can request the certificate for any lot you hold.
Identity: reading the mass spectrometry line
LC-MS answers a different question from HPLC: is this the right molecule? The instrument measures ions, not neutral molecules, so the reported mass carries a label. [M+H] means the molecule plus one proton, so it reads about 1 Da above the molecular weight. Larger peptides often pick up two or three protons and appear as [M+2H] or [M+3H] at roughly a half or a third of their mass: a peptide of about 4,730 Da shows up near 2,367 and 1,578. Other labels such as [M+Na] are adducts, where a sodium or similar ion attached instead of a proton. One rule follows directly: a detected [M+H] can never be lower than the molecular weight. If it is, the ion is mislabelled or a figure is mistyped.
Quantity: label claim, measured content and peptide content
The certificates behind our lots report measured content against the label claim: the laboratory weighs what is actually present and states it next to what the label says. A 10 mg claim measured at 10.1 mg means the vial holds what it states. Some laboratories instead report peptide content, a percentage of net weight that is peptide as opposed to counterion, water and salts. The two are different measurements and should not be compared directly. For concentration work, start from the measured figure; if a certificate gives peptide content, apply it as well. Some laboratories also report water content or solvent traces; the certificates behind our lots do not include those assays.
Endotoxin, and what a blank means
Endotoxin is measured by the LAL assay and reported in endotoxin units per milligram (EU/mg). It matters most for cell-based work, where bacterial endotoxin can affect results independently of the peptide. Not every lot is tested for it. On our lot pages an endotoxin figure appears only when the laboratory measured it; where it was not tested, no figure is shown. A blank means not measured. It does not mean zero.
Errors we have found on real certificates
Every certificate we receive is read line by line before its results go on the site, and genuine laboratory certificates do contain mistakes. The kinds we have caught: a lot number with two digits transposed; the same certificate ID printed on reports for two different products; a label-claim field that contradicts the sample name on the same page; a detected [M+H] lower than the stated molecular weight; a results table describing a molecule roughly ten times the size of the one named; a purity header giving one detection wavelength while the chromatogram shows another; a test date earlier than the date the sample was received; and a copper peptide reported at the mass of its copper-free form. None of these is visible from a purity figure alone, which is why the whole certificate is worth reading. Where an error could mislead, we hold the results back until the laboratory issues a corrected certificate.
Red flags on any certificate
Identical purity figures across several different compounds suggest numbers are being written rather than measured, since real results vary. A certificate with no named laboratory cannot be verified. One with no date, or dates in an impossible order, cannot be matched to a batch. A lot number that does not appear on the product, or the same certificate supplied for material bought months apart, is decorative rather than evidential. Low-resolution images where the figures cannot be read should be treated as absent.
Independent testing means the lab has no stake in the result
In-house quality control is a normal part of manufacturing, but it is not independent verification. What matters is whether the laboratory performing the analysis has a commercial interest in the outcome. A certificate should name the testing laboratory. If the manufacturer and the tester are the same entity, the certificate is a self-report, which may still be accurate but is a different category of evidence and should be described that way.
Sources
The answers under Frequently asked were checked against these sources on 20 October 2026.
- ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories
- FDA Office of Generic Drugs: Assessing Immunogenicity Risk of Peptides, the Synthetic Peptide Guidance and PSGs
- Moore JV et al., Impact of counterion and salt form on the properties of long-acting injectable peptide hydrogels for drug delivery, Royal Society of Chemistry, 2025 (DOI 10.1039/d4fd00194j)
- FDA: Pyrogen and Endotoxins Testing, Questions and Answers (Edition 2, March 2026)
Frequently asked
What purity should research peptides meet?
Most published research uses material at 95% or higher by HPLC, with 98% or more typical for quantitative work. The right threshold depends on the assay: work sensitive to truncated sequences needs higher purity than qualitative screening.
What does 99% HPLC purity mean for a peptide?
It means the target peptide accounts for 99% of the UV-absorbing material the HPLC detected, usually at 214 nm. The remaining 1% is related impurities, such as truncated, deletion or oxidized versions of the sequence. The figure has limits. It doesn’t count water, salts or counter-ions, which don’t absorb at that wavelength. It doesn’t measure endotoxin. And it doesn’t prove identity: a 99% peak could be the wrong peptide, which is why mass spectrometry is run alongside it. What the last 1% contains can matter as much as the headline number. In FDA’s framework for generic synthetic peptide drugs, any new impurity above 0.5% is not acceptable, and new impurities between 0.10% and 0.5% have to be identified and justified. Whether 99% is enough depends on the experiment, but the chromatogram shows more than the percentage does.
Why is the detected mass higher than the molecular weight?
Mass spectrometry measures ions. An [M+H] result is the molecule plus one proton, so it reads about 1 Da above the molecular weight. A detected [M+H] below the molecular weight indicates an error on the certificate.
Why is the measured content slightly different from the label claim?
Filling and weighing carry small tolerances, so measured content usually lands a little above or below the claim. The certificate reports the measured figure so you can work from what is actually present.
What does it mean if no endotoxin result is shown?
The laboratory did not test that lot for endotoxin. A missing figure means not measured, not zero.
Is a COA the same as third-party testing?
No. A certificate documents that testing was performed; it does not by itself establish who performed it. Third-party testing means an independent laboratory with no commercial interest in the result, and the certificate should name it.
What is the difference between peptide content and peptide purity?
Purity tells you how much of the peptide material is the correct sequence. Peptide content tells you how much of the powder’s weight is peptide at all. They measure different things and shouldn’t be compared directly. Purity comes from HPLC. Peptide content is usually measured by elemental (CHN) or amino acid analysis. The rest of the weight is mostly counter-ions left from purification, such as TFA or acetate, plus residual water. In manufacturing, counter-ions are typically measured by ion chromatography and water by Karl Fischer titration. A worked example: 10 mg of powder at 99% purity and 80% peptide content holds about 8 mg of peptide, and 99% of that is the target sequence. A certificate that reports only purity leaves the second number unknown.
What is an LAL test?
An LAL test detects bacterial endotoxin using Limulus amebocyte lysate, a reagent made from horseshoe crab blood cells that clots or changes signal when endotoxin is present. Results are reported in endotoxin units (EU), usually per milligram or per millilitre. There are three main formats, described in USP <85>: gel-clot (a pass/fail clot at a set sensitivity), photometric, and kinetic methods (which read the reaction over time to give a number). FDA has accepted LAL testing in place of the older rabbit pyrogen test for more than 30 years. Its 2026 guidance notes that some biological products still require the rabbit test. Endotoxin is separate from purity. A peptide can be 99% pure by HPLC and still carry endotoxin from its water, glassware or handling. On a certificate, a blank endotoxin field means the test wasn’t run, not that the result was zero.
How can I tell if a peptide COA is real?
A real COA can be traced: it names an independent laboratory that exists, carries a lot number that matches your vial, and is a report the laboratory will confirm it issued. If any of those three checks fails, treat the document as unverified, however good the numbers look. In practice: match the lot (the lot number on the certificate must match the vial label exactly, and the test date should make sense for that lot); check the laboratory (look it up as a registered business with an address and contact, separate from the manufacturer, and if it claims ISO/IEC 17025 accreditation, the international standard for testing-lab competence, confirm it with the accrediting body and check that the tests on the COA fall within the accredited scope); ask the lab (many labs will confirm whether a report number belongs to them); and look for the raw data (a real report shows the HPLC chromatogram and the mass spectrum, not just summary numbers). Red flags: no lot number, the same certificate reused across lots months apart, mismatched fonts or edited images, and a lab you cannot find.
See the practice, not just the principle
Every lot we release is published in full — assay, method, and measured result — and the record stays online after the lot sells out.
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