How to Read a Peptide Certificate of Analysis (CoA): Field-by-Field Guide

What is a Certificate of Analysis?

A Certificate of Analysis (CoA) is a quality-control document that records the identity, purity, and characterisation tests performed on a single batch of material. For peptides, the certificate is produced after synthesis and purification, and it supports batch review through the supply chain so the buyer can compare the available record before opening the vial.

CoAs exist because synthesis is imperfect. Even with careful solid-phase peptide synthesis, batches can contain deletion sequences (missing one or more amino acids), truncations, stereochemical impurities, and residual reagents from the coupling cycle. A CoA quantifies how much of the desired peptide is in the vial relative to those impurities - and confirms that the peptide is actually the one you ordered.

The 8 fields every legitimate peptide CoA includes

Eight fields should appear on every authentic peptide CoA. If any are missing, treat the result as incomplete and ask the supplier for clarification.

1. Product name and amino-acid sequence

The peptide's common name plus the one-letter or three-letter amino-acid sequence. The sequence lets you independently calculate the theoretical molecular weight and compare it with any available molecular-mass result. Acetyl, amide, and PEG modifications should be noted explicitly.

2. Lot or batch number

A unique identifier for one production batch. The same lot number should appear on the vial label, the shipping invoice, and the CoA URL - three independent records pointing to the same lot. If a supplier reuses a lot number across batches, the chain of custody is broken and you cannot trust the documentation.

3. Test date and expiration

When the analysis was performed and how long the result is considered current. Peptide identity doesn't change in the lyophilised vial - but if the supplier holds a batch in inventory longer than 12-24 months, a re-test is warranted to confirm degradation has not occurred.

4. HPLC purity percentage with chromatogram image

Both the number and the visual trace. High-Performance Liquid Chromatography separates the components of a sample by passing them through a column and measuring how long each component takes to elute. The chromatogram shows time on the x-axis and detector signal on the y-axis. The peptide of interest appears as the main peak; impurities appear as smaller peaks. Purity is calculated as the main peak area divided by total peak area. Purity testing is not the same thing as identity confirmation.

For research-grade peptides, the stated HPLC purity percentage should be reviewed together with the full chromatogram and lot record. Below 95% can indicate synthesis problems or substandard purification.

5. Additional identity-specific method, where available

Some CoA packages include an additional molecular-mass method for the relevant batch. When present, it measures the mass-to-charge ratio of resulting ions and reports two numbers:

• Theoretical molecular weight - calculated from the amino-acid sequence.
• Observed molecular weight - measured by the mass spectrometer.

These values should agree within the tolerance stated by the testing lab. A larger discrepancy means the batch record needs review even if the HPLC purity number looks good.

6. Endotoxin and heavy-metals panel

For cell-culture and in-vivo research models, endotoxin and heavy-metal contamination affect experimental validity. Endotoxin is reported in endotoxin units per milligram (EU/mg) or as “not detected” at a specified limit of detection, measured by Limulus amebocyte lysate (LAL) assay. Heavy metals are typically reported as “not detected” or in parts per million (ppm) by inductively coupled plasma mass spectrometry (ICP-MS).

7. Issuing laboratory and accreditation status

The lab that ran the analysis. ISO 17025 accreditation is the international standard for testing-laboratory competence; accredited labs publish a scope of accreditation document listing the specific methods they are certified to perform. Absence of accreditation is not automatically disqualifying, but it removes one verification layer.

8. Verification URL or signature

A way to authenticate the CoA after it leaves the supplier. The best modern practice is a public verification URL hosted on the testing lab's own platform - the page is controlled by the lab, not the supplier, so the result cannot be edited after issuance.

How to interpret HPLC purity numbers

HPLC purity is the most-quoted CoA number, but it's the most easily mis-interpreted as well. Four points matter:

• Peak integration baseline. The chromatogram software draws a baseline below the peaks; everything above that line counts toward integrated area. A baseline that droops or wanders inflates the apparent purity.
• Peak shoulders. A single peptide should produce a single symmetric peak. A “shoulder” on the main peak - a small bump on the leading or trailing edge - indicates a closely related impurity (often a stereoisomer or a deletion sequence) co-eluting and being counted as the main peak.
• Detection wavelength. Peptides are typically monitored at 214 nm (amide bond) or 280 nm (aromatic residues). 214 nm detects more impurities because it's less selective; 280 nm misses peptides without aromatic residues. The CoA should state the detection wavelength.
• Round numbers are suspicious. Real instrumental measurements produce irregular results. 99.00%, 99.50%, 98.00% across consecutive lots is a strong signal of fabricated documentation. Genuine results look like 99.47%, 98.83%, 99.12%.

How to interpret additional identity testing

When an additional molecular-mass method is included, it can support review of whether the record matches the expected peptide. Calculate the theoretical molecular weight from the amino-acid sequence (free online calculators handle this), then compare to the observed mass on the CoA. For a standard instrument, ±1 Da is the acceptable tolerance; high-resolution instruments achieve ±0.5 Da or better.

A discrepancy of 18 Da typically indicates water loss (dehydration); 28 Da indicates oxidation by addition of carbon monoxide; a single amino-acid deletion can show as -57 Da (glycine), -71 Da (alanine), -113 Da (leucine), and so on. Patterns of mass loss tell you what went wrong during synthesis.

Third-party verification vs vendor-internal CoA

A CoA can be issued by the supplier's in-house lab or by an independent third-party testing facility. Both can be technically accurate, but they differ in commercial incentive:

• In-house CoA - produced by the supplier's own analytical chemists. Fast, cheap, but the supplier has a commercial incentive to report favourable numbers.
• Third-party CoA - produced by an independent laboratory under contract. The lab has no stake in whether the result passes or fails; their reputation depends on accurate reporting. The CoA is typically published on the lab's own verification platform, so the result cannot be edited after the fact.

We use third-party lab reporting where applicable for batch-level purity evidence and traceability. Any identity-specific method should be listed only when it exists for that batch.

8 real CoAs from our current catalog

Below are third-party Certificates of Analysis currently linked from the catalog where applicable. Each link opens on the testing lab's own platform. Click through and inspect the available purity evidence, method notes, and lot number directly - the page is hosted by the lab, not by us.

Open any of the URLs above and you see the available lab report evidence, such as HPLC chromatogram, method notes, lot number, and test date, on the testing lab's verification platform. That's the level of traceability a research peptide CoA should aim to provide.

7 red flags that a CoA is fabricated

Fabricated CoAs are common in the gray-market segment of the research peptide industry. Seven signals indicate the document is suspect:

1. Suspiciously round purity numbers. 99.00%, 98.50%, 99.50% across consecutive batches. Real results are irregular.
2. Missing lot number, or a lot number that doesn't match the vial. Lot-to-vial mismatch breaks the chain of custody.
3. No HPLC chromatogram image. Number only, no visual trace - impossible to verify peak shape.
4. Generic “in-house lab” with no name or accreditation. A real lab has a name, an address, and ideally a published accreditation scope.
5. No signature or verification URL. A PDF with no signature and no public link is impossible to authenticate.
6. Identical test dates across multiple products. Suggests the same template was reused and the date wasn't updated.
7. Purity components that sum to more than 100%. Mathematical impossibility - a fabrication error that occasionally appears when the issuer is sloppy.

How we verify every lot before shipping

Our process is straightforward and visible:

1. Sample is drawn from each new batch.
2. The sample is sent to an independent third-party testing lab for available purity testing and any additional batch testing where applicable.
3. The lab publishes the result on its public verification platform.
4. We ship only after the available batch evidence passes our quality review. Lots that fail the review are discarded - they don't get re-graded or sold at lower spec.
5. Every shipment includes the lot number on the vial. CoA links or batch records are handled online where applicable, not as paperwork in the parcel.

The archive of every active lot is on our lab reports page. If you need a CoA for a peptide that's not yet listed there, email info@peptralabs.com.

Frequently asked questions

Last updated 2026-05-22. Reviewed quarterly.