How to Read a Peptide COA
A Certificate of Analysis (COA) records the laboratory results for a submitted batch sample, including the tests performed and their measured results. You cannot judge a research peptide by looking at the powder, so the COA is the single most important trust document. This guide explains every section, what the numbers mean, and how to spot a weak or fake COA.
A useful peptide COA identifies the tested sample or batch, the laboratory, test date and methods performed. Depending on the experiment, relevant measurements include an HPLC peak-area purity figure and chromatogram, an interpreted mass-spectrometry (MS) result and net peptide content. These are separate measurements; check which are actually reported and required by your assay.
What is on a real COA
1. Identity - Mass Spectrometry (MS)
Measures the submitted sample's molecular mass. The observed mass should match the theoretical mass of the peptide (within a small tolerance).
A matching intact mass supports identification but does not establish amino acid order or stereochemistry. Check which identity method was performed; sequence-sensitive analysis may be needed.
2. Purity - HPLC
High-Performance Liquid Chromatography compares the target peptide with the other peptide-related species in the sample. The figure is an area percentage from the chromatogram, not a share of the powder in the vial: water and counter-ions are not part of it, which is what the net peptide content below is for. Read the reported area percentage and, if supplied, the chromatogram - look for one dominant peak. Many small peaks mean more impurities.
Use an assay-specific acceptance criterion. A percentage alone does not establish identity, peptide amount or suitability for every experiment.
3. Net Peptide Content
The actual mass of peptide versus total powder. The remaining mass can include water, counter-ions, residual solvents or other formulation components. A sample can be 99% pure by HPLC but only ~80% peptide by mass - both numbers matter.
4. Water & Counter-ion Content
Residual moisture (often by Karl Fischer titration) and the counter-ion (commonly acetate or TFA) from the synthesis process. Reported as percentages; useful context for the net peptide figure above.
What the numbers mean
| Field | What good looks like | Why it matters |
|---|---|---|
| HPLC purity | Reported method and chromatogram, assessed against the assay specification | Share of the evaluated chromatographic peak area assigned to the target peak under the reported method |
| MS identity | Observed mass matches theoretical mass | Supports mass consistency; does not alone prove sequence or stereochemistry |
| Net peptide content | Reported for the formulation; distinguish peptide mass from total powder | Actual peptide mass vs total powder |
| Batch / lot number | Identifiers match the supplied lot, or the sample-to-lot link is documented | Links the tested sample to the supplied lot; it does not mean each vial was tested |
| Date + lab | Test date and testing lab named | Traceability and accountability |
How to spot a weak or fake COA
- No identifiable tested sample, or no documented link between that sample and the supplied lot.
- A purity claim with no method named and no HPLC chromatogram - just "99%" written on a page.
- The same COA reused for every order, rather than one tied to your specific batch.
- No stated identity method - chromatographic purity alone does not establish compound identity.
- No test date, no lab name, no analyst or signature.
- A report whose batch, method or issuing laboratory cannot be checked; a scanned PDF alone is not proof of fraud.
- A "100%" claim without the analytical method, reporting precision or detection limits needed to interpret it.
Quick checklist before you trust a COA
See real per-batch COAs
Compare the analytical reports available in our library. Tests differ between reports; match the supplier, compound, size and batch with the vial offered before ordering.
View our lab reportsRelated research resources
Analytical references
Updated 5 October 2026. Sigma-Aldrich peptide quick tips distinguishes gross weight, net peptide content and purity, and describes application-specific requirements.
Quality evaluation of synthetic quorum sensing peptides used in R&D combines chromatographic analysis with MS fragmentation to investigate sample identity and related impurities. Its findings concern the study's samples, rather than the suppliers listed here.
Research Use Only: This guide is informational and describes how laboratory documentation is structured. It is not medical, legal, or investment advice. Baltic BioLabs content and products are for laboratory research purposes only and are not intended for human consumption.