How to Read a Peptide Certificate of Analysis
A certificate is a traceability document before it is a purity number.
Most people read a Certificate of Analysis by looking for the biggest percentage on the page. That number is the last thing that matters. Before a purity result means anything, the certificate has to be tied to the vial in front of you, and the certificate itself has to be real. This guide covers all three checks in the order they should happen, using a genuine two-page certificate from ILS Laboratories as the worked example.
If you only do one thing
Find the lot number on the certificate. Find the lot number printed on the vial in your hand. They must be character-for-character identical.
That single check catches more problems than reading every analytical result on the page. A certificate for a different lot is not evidence about your vial — it doesn't matter how good the numbers on it are, and it doesn't matter that the certificate is genuine. Authenticity and relevance are two separate questions, and the lot number is the only thing that answers the second one.
On the example certificate below, the lot number is GL-010250. If the vial you received does not carry that exact lot number, this certificate — however genuine, however good — is not about your vial.
Gate 1 — Does this certificate belong to this vial?
A vendor publishing certificates is not the same as a vendor publishing your certificate. This gate is about the chain that connects a document to the specific item you're holding. It has four links, and all four have to hold.
The material matches.
The name on the certificate, the name on the label, and the name on the vial all identify the same material. On our example, the certificate says "TB-500 - 10mg" and the client is Glow Aminos. If you bought a TB-500 10 mg vial from Glow Aminos, the first link holds.
The lot matches exactly.
Character for character, including suffixes. The lot number on the example is GL-010250. This is the primary key. Everything else on this page is secondary to it.
The labeled amount matches.
A certificate for a 50 mg item is not evidence about a 100 mg item, even from the same producer under the same lot prefix. Different fill, different batch record. The example certificate is for a 10 mg item.
The vial looks right.
Most certificates include a photograph of the submitted vial. Compare label design, cap colour, and overall presentation against what you received.
Visual checks support the lot number. They never replace it.
What this looks like in practice
Gate 2 — Is this certificate real?
A PDF is trivially editable. An image of a PDF is more trivially editable. This gate is about whether the document can be confirmed against the laboratory that supposedly issued it, rather than against the vendor who published it.
The verification ladder
Resolvable at the lab.
The certificate carries a QR code or access code that opens a record on the laboratory’s own domain. The vendor cannot edit what the lab’s server returns. This is the only rung where verification is fully independent of the seller. The example certificate carries access code UGND8WYP and a verification URL at portal.ils-lab.com — this is rung 5.
Searchable at the lab.
The certificate carries an accession or search code that can be looked up in the laboratory’s public database. Nearly as strong; requires you to type rather than scan.
Named lab, no lookup.
A specific laboratory is identified with contact details and a signatory, but there’s no mechanism to confirm the document from the lab’s side. Honest baseline. Most vendors sit here.
Unnamed lab.
The certificate says "third-party tested" without naming who. Nothing here can be checked by anyone.
Image only.
A picture of a certificate with no identifiers, no signatory, no dates. Treat as marketing material.
Read the accreditation wording exactly as printed
This is where certificates are most often over-read, and where vendors most often over-claim.
The example certificate's footer says testing was performed under an ISO/IEC 17025 quality management system. Read that wording exactly as printed: it describes an internal process, not an accreditation. ISO/IEC 17025 accreditation is granted by a recognised accreditation body, carries a certificate number that can be looked up in that body's public register, and is displayed as the accreditation body's mark on certificates — you'll see marks such as ILAC-MRA alongside the accrediting organisation's logo.
Related phrases that mean different things: ISO 9001 is a general quality-management standard that applies to organisations of any kind and says nothing about testing competence. “GMP” describes manufacturing practice, not laboratory accreditation.
None of these are worthless. They are just not the thing people read them as. If a claim of accreditation matters to you, the accreditation body's register is public — look up the number.
A claim about a laboratory is checkable independently of the vendor making it.
We've found vendors describing their testing lab as accredited when the lab's own certificates carry no accreditation mark at all. In most cases this looks like carelessness rather than deception — someone wrote the testing page from memory. It's still a claim you can verify in about two minutes, and it tells you something about how carefully the rest of the site was written.
Other authenticity features worth checking
| Feature | How to use it |
|---|---|
| Certificate number | Should stay identical across every page of a multi-page document. |
| Accession number | The lab’s internal intake reference. Distinct from the certificate number and from the lot number — three different identifiers, routinely confused. |
| Named signatory | A person with a title, not "Quality Department". |
| Page continuity | Page 2 should reference the same certificate number and lot as page 1. |
| Dates | Received, analysed, issued. Should run in that order and make sense against when the item was for sale. |
Three identifiers, three jobs.
Gate 3 — What do the results actually say?
Only now do the numbers mean anything. The central idea in this section is that each assay answers exactly one question and is silent on every other question. A certificate with one impressive result and seven absent ones is not a strong certificate.
Interactive annotated certificate
This is a genuine Certificate of Analysis from ILS Laboratories for a Glow Aminos TB-500 10 mg sample. Tap any numbered hotspot to see what that field means and how to read it. Switch between page 1 and page 2 using the buttons above the certificate.
| Analyte | Specification | Result | Unit | Status |
|---|---|---|---|---|
| Peptide Purity (HPLC) | \u2265 95.0% | 99.79% | % | PASS |
| Net Peptide Content | Report Only | 10.33 | mg | N/A |
| Identity (HPLC-RTM) | TB-4 | Confirmed | - | PASS |
| Fentanyl Screen | Immunoassay, 50 ng/mL | Not Detected | - | PASS |
| Sample | Purity | NPC | ID | Result |
|---|---|---|---|---|
| Dedicated V0 | 99.77% | 10.27 mg | Confirmed | PASS |
| Conformity V1 | 99.79% | 10.33 mg | Confirmed | PASS |
| Conformity V2 | 99.78% | 10.24 mg | Confirmed | PASS |
| Mean | 99.78% | 10.28 mg | — | — |
| Std Dev | 0.0082% | 0.0374 mg | — | — |
This is a genuine Certificate of Analysis from ILS Laboratories for a Glow Aminos TB-500 10 mg sample. It is shown here for educational purposes. A certificate documents what was tested; it does not establish safety, efficacy, or suitability for any use.
Each assay answers one question
| Assay | What it establishes | What it says nothing about |
|---|---|---|
| Purity (HPLC) | Dominance of the target peak among peptide-related peaks under the stated method | Identity, quantity, sterility, endotoxin, elemental contamination |
| Identity (MS / retention time) | That the material is what the label claims | How much of it there is, or what else is present |
| Net content | The measured amount in the tested vial | Whether other vials in the batch match it |
| Conformity | Whether multiple vials from the batch agree with each other | Anything about a batch that wasn’t sampled |
| Sterility | Absence of viable microbial growth under the stated method | Chemical purity, endotoxin burden |
| Endotoxin | Bacterial endotoxin burden | Sterility — these are genuinely different tests |
| Heavy metals | Elemental contamination against a stated limit | Organic impurities, process residues |
| Adulterant screening | Absence of the specific substances screened for | Anything not on the screening list |
“Sterile” and “low endotoxin” are not the same claim.
Reading a purity figure without over-reading it
A purity percentage is a measurement made under specific conditions, not a universal statement about a vial.
It's calculated by area normalisation — the target peak as a proportion of total peak area detected under that method, at that wavelength. The example certificate reports 99.79% purity by RP-HPLC at 214 nm. Note 5 on page 2 explicitly states that non-peptide process-related impurities, if detected, are excluded from the calculation. Material that doesn't absorb at 214 nm doesn't appear in the figure at all.
Many laboratories also cap reported purity at a ceiling such as 99.9% because that's the instrument's limit of detection. A result at the cap means “nothing further was detectable,” not “nothing further is present.”
The practical consequence: purity figures between about 99.0% and 99.9% are not meaningfully rankable against each other. The example's 99.79% and a hypothetical 99.51% are, for any purpose you have, the same result. What actually separates certificates is how many other questions they answer.
Net content, and why underfill is worth looking for
The labeled amount is a claim. The net content result is a measurement. Comparing them is one of the fastest quality signals available on a certificate, and it's the field most readers skip.
On the example certificate, the labeled content is 10 mg and the measured net peptide content is 10.33 mg. That is modest overfill — normal and generally a good sign. Producers target a small excess so that ordinary fill and analytical variation don't leave a vial below its claim.
Underfill is a different matter. It means the vial contained less than the label claimed, and a high purity result alongside it can create false confidence: the material was clean, there was just less of it than stated.
What good disclosure looks like
That certificate is evidence of a real fill problem, and we scored it as one. It is also the strongest available evidence that the rest of their library isn't curated. A certificate archive with no misses in it either means flawless production or means someone is filtering — and from the outside you cannot tell which. This vendor removed the ambiguity.
Conformity: one vial versus the batch
Every result discussed so far describes one tested vial. Conformity testing asks the next question: does the rest of the batch look like that vial?
The example certificate reports three samples: a dedicated vial (V0) plus two conformity vials (V1, V2). Purity results are 99.77%, 99.79%, and 99.78%, with a mean of 99.78% and a standard deviation of 0.0082%. That tight spread is a claim about the batch, not just one vial. A single-sample certificate would leave the batch unaddressed.
This is currently the sharpest dividing line between otherwise similar vendors. Two producers can both report 99.5% purity from the same accredited laboratory; only one of them can show you that four other vials from the same batch agreed. For a deeper look at how we weigh this, see our vendor rankings.
What a spread tells you.
The limitation statement
Near the bottom of most certificates, in the smallest type on the page, sits a paragraph explaining what the laboratory is and isn't asserting. Note 7 on page 2 of the example certificate says three things:
The results apply to the samples submitted. Not to every vial ever produced under that lot, and not to anything the laboratory didn't receive.
Descriptive information was supplied by the client. Product name, labeled content, and lot number came from the submitting party. The laboratory measured what was in the tube; it did not independently confirm what the tube was called.
A test result is not an endorsement. It doesn't validate a manufacturing process, certify a facility, establish safety, or change a product's research-use-only status.
That third point is why controlled sampling and conformity testing matter. The laboratory tests what it's given. Everything upstream of the tube is the producer's responsibility, and the certificate is silent on it.
Common red flags
These are the problems that should stop you before you get to the numbers. Each one means a specific question is open — not necessarily that the product is bad, but that you cannot answer the question from the document in front of you.
Lot number mismatch
The lot number on the certificate does not match the one on your vial. This is the single most important check. A certificate for a different lot is not evidence about your vial, no matter how good the numbers are.
Unnamed laboratory
The certificate says "third-party tested" without naming who. Nothing on it can be checked by anyone. A named lab with contact details is the minimum baseline.
Purity without identity
A purity percentage tells you how dominant the target peak is. It does not confirm the material is what the label claims. A certificate needs both purity and identity (usually by MS or retention-time matching).
Missing net content
The labeled amount is a claim. The net content result is a measurement. If the measurement is absent, you cannot tell whether the vial holds what the label says. This is the field most readers skip.
Single-sample, no conformity
Only one vial was tested. The certificate makes a claim about that vial, not about the batch. Without conformity testing across multiple vials, batch consistency is unknown.
No verification path
No QR code, access code, or accession number that resolves at the laboratory’s own domain. You are trusting the vendor’s PDF with no way to confirm it against the lab.
What a missing test leaves unresolved
| Missing or mismatched | What stays unknown |
|---|---|
| Lot number match | Whether this document describes your vial at all |
| Identity | Whether the material is what the label claims |
| Purity | Whether related impurities or degradation products are present |
| Net content | Whether the vial holds the amount stated |
| Conformity | Whether the rest of the batch resembles the tested vial |
| Sterility | Whether viable organisms are present |
| Endotoxin | Whether bacterial endotoxin burden is within limits |
| Heavy metals | Whether elemental contamination is present |
| Adulterant screening | Whether specific substances of concern were looked for |
| Issue date | Whether the document describes current inventory |
| Verification path | Whether the document is genuine at all |
None of these gaps means a product is bad. Each one means a specific question is open. The useful posture is knowing which questions a given certificate has answered and which it has left alone.
The verification checklist
Gate 1 — Traceability
Gate 2 — Authenticity
Gate 3 — Interpretation
Stop when something doesn't match.
Vendors whose COAs clear all three gates
Every vendor in our database is scored on panel breadth, verification path, and batch integrity — the same three checks this guide walks through. See which ones publish certificates that hold up.
Frequently asked questions
What is a COA?
A Certificate of Analysis (COA) is a document issued by a testing laboratory that reports the analytical results for a specific sample. It identifies the material, the lot number, the tests performed, and the results. It is a traceability document first and a purity number second.
How do I verify a COA is real?
Look for a verification path that is independent of the vendor. The strongest form is a QR code or access code that resolves at the laboratory’s own domain. You can also check that the laboratory is named with contact details, that a signatory is identified, and that the COA number and lot number are internally consistent across all pages.
What is the difference between purity and identity?
Purity measures how dominant the target peptide is among all peptide-related peaks detected by HPLC. Identity confirms that the material is what the label claims, usually by mass spectrometry or retention-time matching. A certificate needs both: purity tells you how clean it is, identity tells you whether it is the right thing at all.
What does "not detected" mean on a COA?
"Not detected" means the test did not find the substance above the method’s limit of detection. It does not mean the substance is absent in an absolute sense, and it says nothing about substances that were not on the screening list.
Is sterility the same as low endotoxin?
No. Sterility testing checks for viable microbial growth. Endotoxin testing measures bacterial cell-wall fragments that survive after bacteria are dead. A sample can pass sterility and still carry endotoxin burden. These are two separate tests reported on two separate lines.
What does conformity testing show?
Conformity testing compares results across multiple vials from the same batch. A certificate that reports a dedicated sample plus additional conformity vials, with a mean and standard deviation, is making a claim about the batch. A single-sample certificate is only making a claim about one vial.
Can a COA guarantee safety?
No. A COA reports analytical results for the specific samples submitted. It does not validate a manufacturing process, certify a facility, establish safety, or change a product’s research-use-only status. The limitation statement on the certificate says this explicitly.
Why does my COA show 99% purity?
A purity percentage is measured by HPLC area normalization at a specific wavelength. It represents the target peak as a proportion of all peptide-related peaks. Many labs cap reported purity at 99.9% because that is the instrument’s limit of detection. Figures between 99.0% and 99.9% are generally not meaningfully rankable against each other.
Read in this order
First, confirm the certificate belongs to the vial. Second, confirm the certificate is real. Third, read what the results say — and what they leave unsaid.
Nearly everyone does this backwards, starting with the purity figure and never reaching the other two. The number at the top of the page is the least informative thing on it.
See how vendors compare on testing
We score every vendor on panel breadth, verification path, and batch integrity.
How our scoring works
The full weighting behind Purity & Testing and the other five categories.
Peptide handling reference
Storage, stability, and reconstitution reference for research peptides.