Hub · Peptide Quality & Verification
How to read a certificate of analysis (COA)
01What it isContents
You hold a small vial in one hand and a sheet of paper in the other. Before any number on that sheet means anything, one string of characters has to match: the lot number — the code for one production run, also called a batch — printed on the label must be the same string printed at the top of the certificate. Until those two strings agree, every figure on the page describes somebody else's material.
This page, part of the peptide quality & verification hub, walks through that sheet line by line: what each field records, what a purity percentage proves, and where the paperwork stops. Purity usually arrives as an HPLC area percentage — HPLC (high-performance liquid chromatography) is a method that separates a mixture so each component shows as its own peak. Two questions run through the whole page: identity (whether the molecule is the one named on the label) and purity (how much of the measured signal is that molecule).
Key facts
| Document type | The test record for one batch — one production run, one sheet |
|---|---|
| Issued by | The manufacturer's quality unit, dated and signed |
| Lot number | The string that ties a physical label to this exact document |
| Lists | Each test performed, its acceptance limits, and the numerical results |
| Identity line | Whether the molecule is the one the label names |
| Purity line | How much of the measured signal is that molecule (usually an HPLC area percentage) |
| Does not show | Safety, regulatory approval, or fitness for any human use |
What is a certificate of analysis?
A certificate of analysis is the dated, signed test record for a single batch, listing each test performed with its acceptance limits and the numerical results obtained. The International Council for Harmonisation describes exactly this record in ICH Q7 (2000), its good-manufacturing-practice guide for active pharmaceutical ingredients, in clauses 11.40 through 11.43. One batch gets one sheet: the document belongs to a single production run rather than to the product line as a whole. That is why the sheet travels with the material it describes. A reader who grasps that pairing — one run, one record — already understands what the rest of the page unpacks.
The guide expects a record for every batch, available on request, because a test result only describes the material actually tested. A product line can run for years, while a batch is one bounded run, and only the sheet carrying its number speaks for it. Published papers, such as those collected in the retatrutide research guide, describe a compound across trials, while a certificate speaks for a single production run.
What should a certificate of analysis include?
A complete batch certificate names the product and its grade, carries the batch number plus the release date and an expiry or retest date, lists every test with its acceptance limit and numerical result, and is dated and signed by quality-unit personnel who name the original manufacturer — and, where a repacker or reprocessor did the testing, name that party too (clause 11.43). ICH Q7 (2000) sets out that contents list in clauses 11.41 through 11.43. A bare word such as 'conforms' tells less than a result printed next to its limit. The signature line matters because it names a person and a unit willing to stand behind the numbers.
The manufacturer line is where origin enters the picture: the sheet should name who made the material and who handled it afterwards, since each production run has its own history. The story of where tirzepatide comes from shows how much origin can matter for a peptide. The check itself is concrete — a buyer comparing the label on a container of retatrutide reference material against the batch number on its sheet is performing the exact match this page opened with.
Does a COA prove identity or purity?
Identity and purity are two different tests that do not prove each other. Identity asks whether the molecule is the one named on the label and needs a method able to tell closely related structures apart; purity asks how much of the measured signal is that molecule. ICH Q6A (1999) states the point bluntly in section 3.2.1: identification by a single chromatographic retention time alone is not regarded as specific. Guidelines therefore accept HPLC combined with MS — MS (mass spectrometry) is a method that weighs a molecule and its fragments — because the two methods separate on different principles. One peak position never identifies a molecule by itself.
A sequence implies a mass, and a mass is something MS can check, which is why orthogonal testing pairs the two. The reference-standard work published in Pharmaceutical Research in 2023 shows the pattern: retention time plus a single co-eluting peak plus full MS/MS sequence coverage (McCarthy et al., Pharmaceutical Research, 2023). The same logic applies at the registry level, where the retatrutide molecular-formula record ties a sequence to a checkable mass. Two methods, two principles, one verdict.
Can a certificate of analysis be wrong?
A COA purity claim can fail independent re-testing. In a study of 98 synthetic research peptides, every peptide arrived with a supplier certificate stating at least 95.0% purity, yet in-house testing found only 43 of the 98 actually met that specification (Verbeke et al., Journal of Pharmaceutical Analysis, 2015). The Journal of Pharmaceutical Analysis paper ordered its peptides before October 2014 from two international suppliers and re-tested them with 2014–2015 in-house methods. The gap between paperwork and measurement is therefore documented, not hypothetical. A percentage on a sheet is a claim about a run, and claims can miss.
The method changes the number. One peptide in the study read at least 95.0% on the supplier's system and 80.6% on the researchers' own system (Verbeke et al., Journal of Pharmaceutical Analysis, 2015). The cyclic subset ran lowest, with none above 90.0% in-house (Verbeke et al., Journal of Pharmaceutical Analysis, 2015). A percentage without its method — column, solvents, gradient, wavelength — is hard to compare across systems. The sheet states a result; the method states what the result means.
Is purity the same as peptide content?
A headline purity percentage is not the peptide content by weight. Purity is a share of the detector signal, while salt counter-ions, water, and residual solvents take up real mass — so the mass-balance work in the 2023 Pharmaceutical Research reference-standard study shows a weighed portion of material holding less peptide than its total weight suggests (McCarthy et al., Pharmaceutical Research, 2023). The share of signal and the share of mass answer different questions. A sheet that reports only the first leaves the second unanswered. Identity, purity, and content are three separate questions, and one number never answers all three.
The plate at the top of this page answers one of the three: purity, the share of signal. Content by weight needs its own accounting, and identity needs its own orthogonal proof. A reader who keeps the three questions separate will read every certificate more accurately than one who lets a single percentage stand for all of them.
Evidence limits
What has research not shown about certificates of analysis?
Published evidence does not show that a certificate of analysis demonstrates safety, regulatory approval, or suitability for human use. A certificate documents one batch's tests and nothing beyond them: no cited evidence turns a passing sheet into proof that a material is safe, approved, or fit for any human use. The one re-testing study on record covers 98 quorum-sensing peptides ordered before October 2014, not any 2026 catalogue (Verbeke et al., Journal of Pharmaceutical Analysis, 2015). ICH Q7 and ICH Q6A are guideline expectations for pharmaceutical manufacture, not studies, and they do not address research-use-only catalogues.
The USP reference-standard work characterises reference standards, not commercial lots, and its mass-balance example is a theoretical illustration (McCarthy et al., Pharmaceutical Research, 2023). Research-use-only material is not a medicine, is not a substitute for any medicine, and is not for human or animal use. That boundary is the whole point of the paperwork: the sheet records tests on a batch, and everything beyond the tests remains unshown.
Comparison
Field by field: what each line of a batch certificate can establish, and what it cannot. A generic sketch — not a real, supplier, or Form Laboratories certificate.
| COA field | What it can show | What it cannot show |
|---|---|---|
| Product name + batch/lot number | Which production run this sheet describes | That the container in hand came from that run (label must match) |
| Release date + expiry/retest date | When the batch passed tests and until when the maker stands behind them | Whether storage since then was proper |
| Identity test line (e.g. HPLC + MS) | Whether the molecule matches the named one, when methods are orthogonal | Identity from a single retention time alone |
| Purity line (HPLC area %) | How much of the signal was the target molecule, by that method | Peptide content by weight, or results by a different method |
| Signature, date, manufacturer details | Who tested the batch and who made it | Anything about safety or approval |
FAQ
What does COA stand for?
COA stands for certificate of analysis: the batch's test record, issued per lot with tests, limits, and results. The letters name a document tied to one production run, not a product line. Without a matching lot number, the record describes somebody else's material.
What does 95% purity mean on a certificate of analysis?
A 95% purity line is an HPLC area percentage: about 95% of the measured signal was the target molecule, by that method, in that run. The HPLC-method framing follows ICH Q6A and the orthogonal-testing pattern in Pharmaceutical Research (McCarthy et al., Pharmaceutical Research, 2023). A supplier claim can still miss: in-house re-testing found only 43 of 98 supplier-certified peptides actually met a claimed 95.0% purity (Verbeke et al., Journal of Pharmaceutical Analysis, 2015).
How do I verify a certificate of analysis?
Verification starts with the lot number on the label: the string must match the sheet exactly. The reader then checks the date and signature, confirms each test shows a limit and a numerical result, and checks that the manufacturer is named. Each step is small, and together the steps tie one container to one record.
Is a certificate of analysis enough to prove a product is genuine?
A certificate of analysis is the maker's own batch record, not independent proof. Identity needs orthogonal tests, and the one published re-testing study found 55 of 98 supplier-certified batches below their claimed 95.0% purity (Verbeke et al., Journal of Pharmaceutical Analysis, 2015). The sheet is evidence from the maker, and evidence from the maker has limits.
Part of
Peptide Quality & VerificationHow research peptide material is tested, what a certificate of analysis actually records, and how a buyer checks that a vial matches its paperwork. Every article in this hub is about verification, not about use.
Citations
2 sourcesVerbeke F et al. Journal of Pharmaceutical Analysis. 2015;5(3):169-181.
doi:10.1016/j.jpha.2014.12.002McCarthy D et al. Pharmaceutical Research. 2023;40(6):1317-1328.
doi:10.1007/s11095-023-03493-1
Form Laboratories supplies research-use-only reference material. This article is an educational summary of published third-party literature. It is not medical advice, not a use instruction, and research material is not for human or animal use.