1. What a COA Is (and Isn't)
A Certificate of Analysis (COA) is a document issued by a laboratory that reports the results of testing performed on a specific batch of a product. For peptides, a COA typically reports purity (how much of the sample is the intended compound) and identity (whether the compound is what the label says it is).
What a COA is not: a guarantee of safety, efficacy, or regulatory compliance. A COA tells you what the lab found in the sample it received. It does not tell you whether the product was stored correctly after testing, whether every batch is consistent, or whether the compound is appropriate for any particular use.
The value of a COA depends entirely on two things: who performed the test (an independent third-party lab vs. the manufacturer's own QC department) and whether you can verify it (more on this in section 7).
2. Anatomy of a COA
A well-structured COA contains several distinct sections. Here's what to look for in each:
Header / Lab Information
The name, address, and contact information of the testing laboratory. A legitimate COA always identifies the lab clearly. If there's no lab name or it's vague (“tested by an independent lab”), that's a problem.
Sample Identification
The compound name, batch or lot number, date received, and date tested. The batch number is critical — it ties the COA to a specific production run. Without it, there's no way to confirm the COA corresponds to the product you're looking at.
Test Results
The core of the document. For peptides, this typically includes HPLC purity (a percentage), mass spectrometry results (observed vs. expected molecular weight), and sometimes additional tests like endotoxin, sterility, or residual solvent analysis. Each result should state the method used.
Lab Reference / Report Number
A unique identifier assigned by the lab to this specific report. This is what you use if you contact the lab to verify the COA is genuine. Not all labs make this easy, but the reference number is your starting point.
3. HPLC Purity: What the Number Means
HPLC (High-Performance Liquid Chromatography) is the standard method for measuring peptide purity. The result is expressed as a percentage — for example, 98.5%.
That number represents the proportion of the sample that is the target compound, as measured by the UV absorbance of separated components. The remaining percentage consists of impurities: truncated sequences (peptides that didn't form completely during synthesis), deletion sequences, oxidized forms, or other byproducts.
What purity levels mean in practice
- >98% — Research grade. Standard for most peptide suppliers making quality claims.
- 95–98% — Acceptable for many applications. Common in commercial peptides.
- 90–95% — Lower grade. May contain significant impurities. More common in bulk or economy products.
- <90% — Crude or poorly purified. Unusual for a finished retail product to report this openly.
Common misunderstanding: HPLC purity tells you how much of the sample is the target peptide. It does not tell you whether the peptide is correctly folded, biologically active, or free from non-peptide contaminants like endotoxins or heavy metals. Those require separate tests.
Another nuance: HPLC results can vary slightly depending on the column, gradient, and detection wavelength used. A peptide that tests at 98.2% in one lab might test at 97.8% in another. Small differences between labs do not necessarily indicate a problem — the methodology section of the COA should specify the conditions used.
4. Mass Spectrometry: Identity Confirmation
While HPLC tells you how pure a sample is, mass spectrometry (MS) tells you what it is. The instrument measures the molecular weight of the compound and compares it to the expected value for the target peptide.
A COA will typically report an observed molecular weight and an expected (theoretical) molecular weight. If they match within the instrument's margin of error, the identity is confirmed — the compound is what it claims to be.
Why this matters: A peptide could test at 99% purity by HPLC but be the wrong compound entirely. HPLC measures how much of the sample is a single substance — it doesn't know which substance. Mass spec provides the identity check. This is why a credible COA includes both tests.
The most common MS techniques for peptide analysis are ESI-MS (Electrospray Ionization) and MALDI-TOF. ESI-MS is more common for smaller peptides; MALDI-TOF is often used for larger ones. Both are standard in third-party testing labs.
5. Other Tests You May See
Beyond HPLC and MS, some COAs include additional testing. These are less common but provide a more complete picture of product quality:
Endotoxin Testing (LAL)
Measures bacterial endotoxin levels. Particularly important for injectable peptides. Results are reported in EU/mg (Endotoxin Units per milligram). Lower is better — the USP limit for injectable products is typically 5 EU/kg of body weight per hour.
Sterility Testing
Confirms the absence of viable microorganisms. Relevant for products sold as sterile. This is a pass/fail test, not a measurement.
Amino Acid Analysis (AAA)
Breaks the peptide into its individual amino acids and measures their ratios. Confirms the peptide sequence composition. Less common on standard COAs but provides strong evidence of correct synthesis.
Residual Solvent Analysis
Checks for leftover solvents from the synthesis and purification process (e.g., TFA, acetonitrile, DMF). Important because some solvents are toxic above certain thresholds.
6. Red Flags in a COA
Not all COAs are created equal. Here are specific things that should raise questions:
A COA that doesn't name the testing laboratory is unverifiable. "Tested by an independent lab" without a name is meaningless.
Without a batch number, there's no way to confirm the COA corresponds to the specific product you purchased. The same COA could be reused across different batches.
A purity number without the method used (HPLC column type, gradient, detection wavelength) makes the result impossible to evaluate or reproduce.
Real lab results rarely land on perfectly round figures. A COA reporting exactly 99.00% purity across every product is unusual. Legitimate results typically include decimal variation (98.47%, 97.82%, etc.).
Purity without identity confirmation means you know the sample is pure — but pure what? A credible COA for peptides includes both HPLC and MS.
Multiple generations of copying can obscure details and make verification harder. It can also indicate the document has been altered. Look for original digital reports or first-generation scans.
If a supplier shows COAs for 15 different compounds all tested on the same day, that's not impossible — but it's unusual enough to warrant verifying with the lab.
7. How to Verify a COA Is Real
A COA is only useful if it's authentic. Here's how to check:
Contact the lab directly
The most definitive verification. Use the lab reference number from the COA and contact the laboratory through their official website — not through a link on the supplier's site. Ask them to confirm the report exists and matches the details shown. Reputable labs like Janoshik Analytical will confirm or deny whether a report number is genuine.
Cross-reference the batch number
The batch number on the COA should match the batch number on the product label or packaging. If the product doesn't have a batch number displayed, that itself is a concern — there's no way to tie the COA to the specific product.
Use a certificate tracking platform
Some suppliers register their lab results on public certificate tracking platforms that issue unique, QR-verifiable certificate IDs. This creates an auditable trail: you can verify that a specific product batch was registered with specific lab results at a specific point in time.
For example, here's a live, verifiable certificate on Certivos: View certificate CV-2026-0055. Each certificate page shows the compound, batch, testing lab, test date, and links back to the original lab report data.
Check the lab's reputation
Not all labs are equal. A COA from a well-known, frequently cited third-party lab carries more weight than one from an unknown or in-house facility. Our Lab Directory profiles testing laboratories and their methodologies.
The Bottom Line
A COA is only as trustworthy as the lab that produced it and your ability to verify it. When evaluating a peptide supplier, look for: third-party lab testing (not just manufacturer QC), both HPLC purity and mass spec identity confirmation, verifiable batch numbers, and a clear path to confirm the report is genuine. If any of those pieces are missing, ask the supplier why.