A certificate of analysis is a lab report on one sample from one batch. A complete one shows four things: identity by mass spec, purity by HPLC, how much of the powder is peptide, and endotoxin and sterility results. Most research-peptide certificates show only the first two, and none of them can tell you what happened to your vial after the test.
11 minute read 9 sources Reviewed October 2026
The four questions a certificate should answer
1IdentityIs it the right molecule?Mass spectrometry
2PurityHow much of the peptide is the intended sequence?HPLC
3ContentHow much of the powder is peptide at all?Nitrogen or amino acid analysis
4SafetyCould it cause fever or infection if injected?Endotoxin and sterility
Field by field
An annotated sample certificate
Tap any numbered field. Then switch to the weak version to see the same certificate the way many sellers publish it, with each gap marked.
Tap a numbered field
TEACHING SAMPLE
CERTIFICATE OF ANALYSIS
Field 3 of 8
How pure the peptide is
High-performance liquid chromatography separates the sample, and a UV detector draws a peak for each component. Purity is the main peak's area divided by the area of every peak.
What good looks likeThe method is stated and the chromatogram is attached, so you can see the main peak and the small impurity peaks yourself.
Field 3 of 8
How pure the peptide is
High-performance liquid chromatography separates the sample, and a UV detector draws a peak for each component. Purity is the main peak's area divided by the area of every peak.
What good looks likeThe method is stated and the chromatogram is attached, so you can see the main peak and the small impurity peaks yourself.
This certificate is invented for teaching. The lab, lot and reviewer do not exist. The masses are real: BPC-157 has an average molecular mass of about 1,419.5 Da.
Purity
What the HPLC number does and does not measure
Worked example: how 98.6% is calculated
Peak
Area
Share
Main peak (intended peptide)
9,860
98.6%
Impurity A (shorter sequence)
84
0.8%
Impurity B (oxidized form)
56
0.6%
Total of all peaks
10,000
100%
Purity = 9,860 / 10,000 = 98.6%. The areas are illustrative.
HPLC pushes the dissolved sample through a packed column. Different molecules come out at different times, and a UV detector draws a peak for each one. The certificate's purity number is the main peak's share of the total peak area.
Four things it cannot see
Water and salts, which have no UV signal, so a 98% pure powder can still be 20% water and acetate by weight.
Impurities that come off the column at the same time as the main peak and hide inside it.
A completely different peptide, if it happens to elute where the expected one should. That is the job of mass spec.
Bacteria and endotoxin. Purity is a chemistry number, not a safety number.
What purity numbers mean in different settings
Use
Typical purity reported
What else is required
Approved peptide drug
Set by the approved specification
Identity, assay, named impurity limits, sterility, endotoxin, every batch
FDA generic synthetic peptide (2021 guidance)
New impurities each under 0.5%
Any new impurity above 0.10% must be identified
Lab research reagent
Often listed at 95% to 98% or higher
Usually only HPLC and mass spec
Crude synthesis product
Can be well under 70%
Purification needed before any use
Identity
Mass spec: weighing the molecule
The instrument gives molecules an electric charge and measures mass divided by charge (m/z). A peptide can pick up one, two or three protons, so one molecule shows up as several peaks.
BPC-157, average mass 1,419.5 Da
The arithmetic
(1,419.5 + 2 × 1.008) ÷ 2 = 710.8
The 2+ peak sits at about half the molecule's mass plus two protons. Divide by 3 for the 3+ peak, and so on. A good certificate reports the observed mass after this conversion and compares it with the expected mass.
What mass spec catches
The small amber peak at m/z 682.3 is what a version missing one glycine would produce: 57 Da lighter, so about 28.5 lower at a 2+ charge. HPLC can miss a deletion like this when it elutes next to the main peak. Mass spec cannot.
Net peptide content
How much of a 10 mg vial is the peptide on the label
Freeze-dried peptide powder holds water and counter-ions as well as peptide. Move the sliders to see how the numbers on a certificate combine.
The math: 10 mg × 82% × 98.6% = 8.09 mg. Some manufacturers fill vials by net peptide content, so the label already means peptide; the certificate should say which. If a certificate gives only HPLC purity, this number cannot be worked out.
Injection safety
Endotoxin and sterility: the two tests most often missing
Bacterial endotoxins
Endotoxin is a molecule from the outer wall of gram-negative bacteria. It survives the processes that kill bacteria, and injected, it can cause fever, chills and a fall in blood pressure.
Test: Limulus amebocyte lysate (LAL) or recombinant factor C, under USP chapter 85.
Result: endotoxin units per milligram (EU/mg), compared with a limit.
The limit depends on the dose and route, which is why a number only means something next to a stated specification.
Sterility
The sterility test places samples in two growth media and watches for bacteria or fungi for 14 days. No growth means those samples were sterile.
Test: USP chapter 71.
Required for every batch of an approved injectable drug under 21 CFR 211.167.
Limit: it samples a few units, so it can miss low-level contamination. Manufacturing controls carry most of the weight.
Why research certificates skip them
A product sold as a lab chemical has no sterility or endotoxin requirement, so these tests are often left off. In a 2024 test-buy study of unregulated semaglutide, and in a 2026 preprint pooling 6,441 peptide test results, endotoxin turned up in a share of samples. A certificate without these two results says nothing about whether a vial is safe to inject.
Your turn
Score a certificate in two minutes
Tick what your certificate shows
Score0/10
Not a usable certificate
A document this thin is a marketing image, not a lab report.
Six red flags
One certificate for every lot
The same report number or chromatogram appears on different products or batches.
Purity of 99% or more on everything
Real synthesis runs vary. A wall of identical round numbers suggests the numbers are not from real runs.
The lab is the seller
An in-house "quality department" with no accreditation cannot be checked by anyone else.
The lab cannot confirm it
Ask the lab directly, using contact details from the lab's own website, whether it issued the report.
Dates that do not fit
A test date before the lot was made, or a report years older than the product.
Edits visible in the file
Mismatched fonts, a lot number pasted over a blank, or a screenshot instead of a PDF.
The limits
What even a perfect certificate cannot tell you
Whether your vial matches the sample
The lab tested a few vials from one lot. Your vial may come from another lot, or the label may not match the lot that was tested.
What happened after testing
Heat, light and time degrade peptides. A certificate dated before shipping says nothing about a vial that sat in a hot mailbox.
Whether it is safe to inject
Even a perfect certificate does not make a research chemical an approved drug, and most research certificates skip endotoxin and sterility.
Whether the peptide does anything
Purity is about what is in the vial. Whether that molecule helps people is a question for clinical trials.
New quality studies, FDA warning letters and recalls, explained with the source linked. Daily and free. We do not sell peptides or rank sellers.
Frequently asked questions
What is a certificate of analysis?
A certificate of analysis, or COA, is a lab report for one batch of a product. For a peptide it usually lists identity by mass spectrometry, purity by HPLC and, on better certificates, peptide content, endotoxin and sterility. It describes the sample the lab tested, not every vial from that batch.
What purity should a peptide COA show?
Research-grade peptides are commonly listed at 95% to 98% or higher by HPLC. The number alone means little without the method and the chromatogram, and purity does not include water or salts in the powder. For approved synthetic peptide generics, FDA guidance expects any new impurity to stay under 0.5%.
What is the difference between HPLC purity and net peptide content?
HPLC purity is the share of the UV signal that comes from the intended peptide. Net peptide content is the share of the powder's weight that is peptide at all, after water and counter-ions such as acetate or TFA. A powder can be 99% pure by HPLC and 80% peptide by weight.
Why does mass spec matter if purity is high?
HPLC shows that the sample is mostly one compound. Mass spectrometry shows which compound by weighing it. A sequence missing one glycine weighs 57 Da less than the intended peptide; mass spec will catch it, while HPLC may not separate it.
What is endotoxin and why does it matter?
Endotoxin is part of the outer membrane of gram-negative bacteria. Injected, small amounts can cause fever, chills and low blood pressure. Sterilizing kills bacteria but does not remove endotoxin, so it has its own test, usually the LAL assay described in USP chapter 85. Research certificates often leave it out.
Can a COA be faked?
Yes. Certificates are often images or PDFs that are easy to edit or reuse. The best check is to contact the testing lab directly, using contact details from the lab's own website rather than the seller's, and ask whether it issued that report number for that lot.
Does third-party testing make a research peptide safe to use?
No. Testing tells you about the chemistry of a sample. It does not make an unapproved product approved, it does not cover how the vial was stored after testing, and it says nothing about whether the peptide works or is safe in people.