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How to Read a Peptide COA
How to read a peptide certificate of analysis: every field, what the numbers mean, and the red flags that signal a fake.
Watch for fakes. Fraudulent certificates are common in the peptide market. A real COA names a specific batch, an identifiable lab, and a dated analytical method. If any of those are missing, treat the document with extra skepticism.
Interactive
COA verification checklist
Open the COA you’re checking and tap what it actually shows on both lists below. This runs entirely in your browser: nothing you tick is sent anywhere.
Red flags
Each red flag = risk.
0/8
Green flags
Each green flag = trust.
0/8
Not started
0 green · 0 red
Tick off what your COA actually shows, on both lists, to get a verdict.
The basics
What is a peptide COA?
A certificate of analysis is a batch-specific document summarizing the analytical results for a particular peptide lot. It’s what connects a physical vial to its identity, purity, content, and contaminant profile: the four things worth knowing before trusting a research peptide.
A good COA answers four questions: Identity (is this the right molecule?), Purity (how chemically clean is it?), Content (how much actual peptide?), and Contaminants (what else is present?).
Our approach
Part of PepLookup’s COA Verification Approach
This reader is one part of how PepLookup approaches certificate verification. Alongside this field guide, our lab reports directory links directly to supplier-published certificates, and every supplier profile notes whether a COA is on file for each listing. Together, these tools help you cross-check claims rather than accepting them at face value.
Every field
Field-by-field breakdown
9 fields
01Product & Lot IdentityDoes the COA identify the exact peptide, lot, and method?
- Peptide name (e.g. BPC-157 acetate) and its amino acid sequence
- Theoretical molecular weight in daltons: should match the MS result
- Lot or batch number that matches the vial label exactly
- Manufacturing date and report date
- Testing laboratory name, address, and analyst
02AppearanceA simple but meaningful check on the physical product.
- Most lyophilized peptides should be a white to off-white powder
- Yellow or brown discoloration can signal oxidation or degradation
- Visible clumping or an unusual texture can point to moisture exposure
- Compare what’s reported here to the product photos and description
03HPLC PurityTells you how chemically clean the sample is.
- Reported as area % at roughly 210–220 nm, where peptide bonds absorb
- 98% or higher is generally treated as the research-grade benchmark
- 95–97% is usually acceptable for most research applications
- Anything under 95% suggests a synthesis or purification issue
- Purity is method-dependent: column, gradient, wavelength and integration settings all affect the number
04Mass Spectrometry (MS)Confirms the molecule actually matches what the label claims.
- MS checks that molecular weight and charge states match the expected peptide
- Look for the expected m/z values at the +2 or +3 charge states
- Major peaks should line up with the theoretical molecular weight
- HPLC tells you how clean it is; MS tells you what it actually is
05Net Peptide ContentHow much actual peptide is in the vial, excluding counterions.
- Expressed as a % of gross weight, after accounting for water, salts and counterions like TFA or acetate
- Typical range is 75–90% for acetate salts
- Matters for dosing math: a vial labeled "10 mg" might contain closer to 8 mg of actual peptide
- Skipping this figure can throw reconstitution calculations off by 10–25%
06Endotoxin TestingBacterial endotoxin testing, most relevant for in-vitro work.
- Reported in EU/mg or EU/mL
- A common research-grade limit is under 1 EU/mg, sometimes up to 5 EU/mg
- Performed with a LAL (Limulus Amebocyte Lysate) assay
- Often missing from bare-minimum COAs: worth requesting directly before in-vitro use
07Heavy MetalsICP-MS screening for residual lead, mercury, arsenic and cadmium.
- Usually reported in ppm (parts per million)
- Should sit below the ICH Q3D limits used for parenteral research material
- Often run as a separate test from the main identity/purity report
- If it’s missing, it’s reasonable to ask the supplier for it directly
08Residual SolventsTrace synthesis solvents like acetonitrile, TFA, or methanol.
- Reported against ICH Q3C guideline classes
- Class 1 solvents (e.g. benzene) should be undetectable
- Class 2/3 solvents (acetonitrile, methanol) have defined allowable limits
- Usually grouped into a single "residual solvents" section on the report
09Dates & Sign-offTraceability and accountability for the report itself.
- Manufacturing date for the lot
- Testing date and report date
- Retest date, if used: typically 1–2 years out for a lyophilized peptide
- Analyst name, QA reviewer, and a document control ID
- Stripped PDF metadata (missing author or lab info) is itself a red flag
Purity
How to Read an HPLC Chromatogram
An HPLC chromatogram is a graph of everything the detector picked up as the sample passed through the column. Time runs along the bottom (retention time, in minutes) and signal strength runs up the side. Each peak is a separate substance, and the target peptide should be the largest one by far.
Purity is calculated from peak areas: the main peak’s area divided by the total area of all peaks. The table below is an illustrative example of how a peak table appears on a COA.
| Peak | Retention time | Area % | What it is |
|---|---|---|---|
| 1 | 3.2 min | 0.4% | Early-eluting impurity |
| 2 | 11.8 min | 98.9% | Main peak (target peptide) |
| 3 | 12.6 min | 0.7% | Related impurity |
| Total | 100.0% |
In this example the reported purity is 98.9%. Small peaks sitting close to the main peak are usually related impurities from synthesis, such as shortened or incomplete sequences. Peptides are normally detected at around 214–220 nm, so check that the wavelength is listed. Remember that HPLC purity describes how clean the material is, not how much peptide is in the vial; that is what net peptide content covers.
Identity
How to Read Mass Spectrometry Results
Mass spectrometry confirms identity by measuring the molecular weight of what is in the sample and comparing it with the peptide’s theoretical weight. If the two match closely, the expected molecule is present. A match does not measure purity, and it cannot by itself confirm the exact amino acid sequence.
The number on a COA often does not equal the molecular weight, which confuses many readers. Mass spectrometers measure mass-to-charge ratio (m/z), and peptides usually pick up one or more protons, so the result may be reported as a charged ion rather than the neutral mass. The illustrative example below uses a peptide with a theoretical molecular weight of 1,419.5 Da.
| Ion reported | How it is calculated | Expected m/z |
|---|---|---|
| [M+H]+ | 1,419.5 + 1.007 | 1,420.5 |
| [M+2H]2+ | (1,419.5 + 2.014) ÷ 2 | 710.8 |
If a COA lists 710.8 for this peptide, that is a match, not an error. What should worry you is an observed mass that matches no reasonable ion of the target, or a COA that gives a single “MW confirmed” line with no spectrum and no numbers.
Next step
Cross-check with published lab reports
Instead of judging a COA image in isolation, cross-check it against the reports suppliers have published for the same compound, and contact the testing lab directly if anything looks off.
Browse lab reportsSummary
Bottom line
HPLC tells you how clean it is. MS tells you what it is. Net content tells you how much. Contaminant tests tell you what else is in it. A complete COA touches all four.
A COA is a research documentation tool, not a medical certificate or a guarantee. Pair it with your own judgment and quality checks rather than treating it as a substitute for either.
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Questions
Frequently asked questions.
What is a peptide certificate of analysis (COA)?
A COA is a lab document reporting test results for one specific batch. A useful peptide COA shows identity (usually by mass spectrometry), purity (usually by HPLC), the batch or lot number, the test date and the name of the lab that ran it.
How do I read HPLC purity on a peptide COA?
The chromatogram shows peaks for each substance detected. Purity is the main peak’s area as a percentage of the total peak area, so 99.1% means the target peptide makes up 99.1% of what the detector picked up. It does not tell you how much peptide is in the vial, or account for water and salts.
What does mass spec show on a peptide COA?
Mass spectrometry confirms identity. It compares the measured molecular weight against the peptide’s theoretical weight, and the two should match closely. It shows the right molecule is present, but on its own it does not measure purity.
How can I tell if a peptide COA is fake?
Warning signs include no batch number or one that doesn’t match the vial, a lab that isn’t named or can’t be contacted, the same report reused across different products or dates, a purity figure with no chromatogram, and numbers that look edited. When in doubt, contact the testing lab directly to confirm the report.
Does a COA guarantee what’s in my vial?
No. A COA only covers the batch that was tested. Check that the batch number matches your vial, the test is recent and the lab is independent of the seller. You can compare suppliers’ published reports on PepLookup’s lab reports page.