Peptide Testing
How to Read a Peptide Certificate of Analysis (COA): Complete Guide
By PRISM Analytical Laboratories · · 9 min read
A Certificate of Analysis (COA) is the most important document you can have for a research peptide. It is also one of the most misunderstood. Many buyers look for one number, usually purity, and miss the details that show whether the vial is genuine, correctly dosed and safe to handle.
This guide goes through a peptide COA section by section, the same way our chemists review one before it leaves the lab.
In this guide:
- What a COA is and who should issue it
- Every section of a peptide COA explained
- Acceptable result ranges at a glance
- Red flags that should make you stop
- How to verify a COA in seconds
What is a peptide Certificate of Analysis?
A COA is a laboratory report confirming the identity, purity, quantity and safety of one specific batch (lot) of a compound. A COA only applies to the lot it names. A report for lot A tells you nothing about lot B, even when the supplier and label are the same.
There are two kinds of COA:
| Type | Issued by | Independence | Trust level |
|---|---|---|---|
| In-house COA | The manufacturer or vendor | None: the seller tests its own product | Low to moderate |
| Third-party COA | An independent lab such as PRISM | Full: the lab has no stake in the result | High |
| Customer-submitted COA | Independent lab, paid for by the buyer | Full, and tied to the exact vial you hold | Highest |
Section 1: Sample information
This section identifies what was tested and when:
- Compound name: the peptide or blend claimed on the label
- Report number: a unique ID used to verify the report
- Lot or batch number: must match the number printed on your vial
- Appearance: for example "white lyophilized powder"
- Received and analyzed dates: results more than 12 months old are unlikely to cover the current stock
If the lot number does not match your vial, the rest of the report does not apply to you.
Section 2: Chromatographic purity (HPLC)
High-Performance Liquid Chromatography (HPLC) separates the sample into its components. Purity is the area of the main peak as a percentage of all detected peaks.
A tall, single main peak with small or no side peaks means high purity. Extra peaks usually come from truncated sequences, deletion by-products or degradation.
| HPLC purity | What it usually means |
|---|---|
| 99% or higher | Excellent, high-quality synthesis |
| 98 to 99% | Standard research grade |
| 95 to 98% | Acceptable for some uses, more impurities |
| Below 95% | Poor synthesis or degraded material |
Section 3: Net peptide content
Net content is the measured mass of peptide in the vial, in milligrams. Compare it with the label claim:
| Label claim | Measured | Fill accuracy | Verdict |
|---|---|---|---|
| 10 mg | 10.2 mg | 102% | Correctly dosed |
| 10 mg | 9.4 mg | 94% | Slightly under-filled |
| 10 mg | 7.1 mg | 71% | Significantly under-filled |
A vial can be 99% pure and still hold far less peptide than advertised. This is why purity alone is not enough.
Section 4: Observed molecular weight (identity)
Mass spectrometry measures the molecular weight of the compound in Daltons (Da). The observed MW should match the theoretical mass of the peptide within a small tolerance. If it does not, the vial may contain a different compound entirely, even when the HPLC purity looks perfect. Read more in our guide to HPLC vs mass spectrometry.
Section 5: Heavy metals
ICP-MS screening checks for the four main toxic elements:
| Element | Symbol | Typical concern |
|---|---|---|
| Lead | Pb | Contaminated reagents or equipment |
| Arsenic | As | Raw material contamination |
| Cadmium | Cd | Industrial contamination |
| Mercury | Hg | Environmental contamination |
Each should read Undetected or Pass against the stated limit.
Section 6: Endotoxins
Bacterial endotoxins are measured with the LAL method and reported in EU/mg. A result below the stated limit is a Pass. This matters most for injectable research material.
Red flags on a COA
- No report ID, or the ID cannot be checked with the lab
- Lot number missing or different from your vial
- Suspiciously round figures such as exactly 100.00%
- Purity shown but no net content or identity data
- A lab name you cannot find or contact
See the full list in how to spot a fake COA.
Verify before you trust
A COA is only as trustworthy as the lab that can confirm it. Every PRISM report has a unique ID that anyone can check on our verification page. If you want results tied to your own vial, see peptide testing in Canada for pricing and turnaround.