How to Read a Peptide COA: Certificate of Analysis Guide
TL;DR · The short version
Start a peptide certificate of analysis review by matching the product and lot. Then work through the results with their methods, units and specifications. Purity, identity and vial content are different questions, so keep the original report with your receiving record and ask about any field you cannot reconcile.
If you want to know how to read a peptide COA, set the vial beside the report before looking at the purity figure. That percentage can be useful, but it doesn’t establish that the document belongs to the material you received. The match comes first.
You can make a useful first pass without being an analytical chemist. Follow the material through the label, results table and supporting evidence, then keep a record of what you checked. The important part is knowing which question each result answers.
Match the vial to the peptide COA
TL;DR: The product name and lot or batch number should connect the physical material to the laboratory report.
First, the lot.
Read the compound name, labeled amount and relevant form or modification on the label, listing and certificate together. Where a sequence, salt form or molecular formula is supplied, include it in the comparison. A similar name can hide a material difference that changes how you read the evidence.
Suppose, hypothetically, that the vial says lot A and the report says lot B. A high purity result for B tells you nothing about A’s result. Keep the document, leave both identifiers as written and request the report for the received vial. Editing a label to make the records agree would conceal the mismatch.
On our product pages, the featured batch-specific COA links to the associated documentation. Confirm that the lot shown there corresponds to your material; a page can change as stock changes. The COA results library also lets you review available reports.
Read across the results table, not just down the percentages
TL;DR: A useful reading joins the test, method, result, unit and stated specification.
Follow one results-table row all the way across. Identify the test and method, then read the result and its unit. Is it a percentage, a mass, a calculated value or a qualitative observation? Finally, find the stated specification used for that comparison. Don’t skip straight from the test name to a number.
Reports use different layouts. This is a reading guide, not a claim that every testing laboratory uses the same fields.
| Report field | What to check | Question it helps answer |
|---|---|---|
| Product and sample identifiers | Compound, amount, lot number and any sample ID | Which material does this record describe? |
| Report number and laboratory | The original document’s identifier and issuing laboratory | Which record should a clarification refer to? |
| Test and method | The measured attribute and named procedure | What does this result actually describe? |
| Result and unit | The value, unit and any reporting qualifier | Is it a mass, percentage or observation? |
| Specification | The limit or description stated for that test | What criterion was applied? |
| Dates and document revision | Sample receipt, test date, issue date or revision, when listed | Which version of the record am I reviewing? |
When you make notes, retain the names of the identifier fields. A sample ID may differ from a batch number, and the report number may identify the document rather than the vial. Keeping those distinctions makes a follow-up question much easier to resolve.
Separate purity, identity and peptide content
TL;DR: A purity result doesn’t establish all the contents of a vial or fully identify its sequence.
HPLC purity commonly expresses the target peak’s share of integrated chromatographic area under the stated method. It isn’t automatically the percentage of all dry material in the vial. Water, counterions and other components can require separate measurements.
Identity asks whether the sample is the intended compound. Mass spectrometry can support that assessment, but a molecular-weight match alone doesn’t resolve every possible sequence or stereochemical difference. Net peptide content is another question: how much peptide is present after accounting for relevant non-peptide components.
Researchers developing peptide reference standards use complementary methods because these measurements serve different purposes. Their 2023 reference-standard study describes identity testing and value assignment in detail. For a fuller explanation of the distinction, see our purity versus identity guide.
Look at the chromatogram and mass evidence in context
TL;DR: Supporting data help explain the reported result; their appearance alone doesn’t authenticate a sample.
If a chromatogram is provided, locate the assigned main peak, the retention time and the calculation or reporting notes. A dominant peak is useful evidence, but you still need its assignment and the method context to interpret it. Agilent’s chromatogram documentation distinguishes compound assignments from retention-time labels. Our HPLC chromatogram guide walks through those features.
For mass data, find the reported mass or molecular weight, its expected value and the laboratory’s explanation of the comparison. Presentations differ across LC-MS and other mass-spectrometry procedures. If the assignment isn’t clear, ask the laboratory or supplier to explain that particular display.
Worth checking before you compare.
Compare the methods, units and reporting bases before deciding whether two COAs agree. A percentage and a milligram result aren’t interchangeable measurements. Copy the field name and unit into your notes with the value instead of collapsing them into a single “quality” score.
Check the original report when a summary raises a question
TL;DR: A branded summary is a convenient view; the linked source report supplies the original wording and qualifications.
The branded summary gives selected source fields a consistent layout. When you need the complete description, notes or identifiers, open the linked original. A cropped image or thumbnail percentage can leave out the detail that answers your question.
Keep both documents if something appears inconsistent. Frame the question with the report number, product name, labeled amount and lot; include a clear label photo where the physical vial is in doubt. A polished layout, logo or familiar purity figure can’t explain away a mismatch between the records.
The Reading a COA guide offers a printable companion for this review.
Keep the COA with your receiving record
TL;DR: Save the matched report, review date and any unresolved question with the material’s lot record.
Record what arrived, its lot, which report you reviewed and when you reviewed it. Our Receiving, Storage & Traceability Record gives you a printable place for those details and later storage events.
A recent test date isn’t an expiry date. Use the applicable material instructions and laboratory procedures rather than deriving a storage period from the certificate’s date. Likewise, an unlisted test shouldn’t be treated as work the laboratory performed.
Order verification and analytical documentation also serve different purposes. An order code can help verify an order record; it doesn’t replace the match between a vial and its COA. Keep private order details out of public notes.
At the end of the review, you should be able to point to the material, retrieve its original report and explain the reported results. Write any remaining uncertainty as a specific question in the review record. That is something the laboratory or supplier can respond to.