How to Read a Peptide COA (and Spot a Fake)
Every reputable research peptide vendor provides a Certificate of Analysis (COA) for each product batch. This document reports the results of analytical testing -- purity, identity, endotoxin levels, and more. It is the single most important quality indicator when comparing vendors.
Most buyers never read COAs. Of those who do, most don’t know what they’re looking at. This guide fixes that.
What a Real COA Contains
A legitimate COA should include at minimum:
| Field | What It Means | Target Value |
|---|---|---|
| HPLC Purity | Percentage of correct peptide sequence vs impurities, measured by high-performance liquid chromatography | ≥98% |
| Mass Spectrometry (MS) | Confirms molecular weight matches the expected peptide sequence (identity verification) | Within 0.1% of theoretical MW |
| Batch/Lot Number | Unique identifier linking the COA to a specific production run | Must match product label |
| Appearance | Physical description (white lyophilized powder for most peptides) | White/off-white powder |
| Endotoxin (LAL) | Bacterial endotoxin contamination level | <0.5 EU/mg |
| TFA Content | Residual trifluoroacetic acid from synthesis (counterion) | Reported (lower is better) |
Red Flags: How to Spot a Fake or Useless COA
- No batch number -- A COA without a unique lot number cannot be traced to a specific production run. It may be a generic template applied to every order.
- No HPLC chromatogram -- A purity percentage without the actual chromatographic trace is unverifiable. Reputable vendors include the raw HPLC plot.
- Purity listed as exactly 99.99% -- Suspiciously perfect numbers suggest the COA was fabricated. Real peptide synthesis always has trace impurities; 98.2% or 99.1% is realistic.
- No mass spec data -- Without MS confirmation, you cannot verify the peptide is what the label claims. HPLC measures purity; MS confirms identity.
- Same COA for every product -- If every peptide in a vendor’s catalog shares identical formatting, batch numbers, or test dates, the COAs may be auto-generated templates.
- No third-party testing option -- The best vendors either use independent labs or will provide samples for third-party verification on request.
What Truncated Sequences Mean
In HPLC analysis of peptide purity, the most common impurities are truncated sequences -- shorter versions of the target peptide where synthesis failed at one or more coupling steps. A COA showing 98% purity with 2% truncated sequences is normal. A COA showing 95% purity with 5% unidentified impurities is a concern.
For research applications, ≥98% HPLC purity is the standard threshold. Below 95%, impurity profiles can confound experimental results.
Vendors That Get COAs Right
The research peptide vendors we recommend all provide batch-specific COAs with HPLC chromatograms and mass spectrometry data:
BioPure Peptides
Research-grade peptides with third-party purity testing and certificates of analysis.
Shop BioPure Peptides →POWER at checkoutMidwest Peptide
Research-grade peptides with third-party purity testing and certificates of analysis.
Shop Midwest Peptide →POWER at checkoutApollo Peptide Sciences
Research-grade peptides with third-party purity testing and certificates of analysis.
Shop Apollo Peptide Sciences →Frequently Asked Questions
A Certificate of Analysis (COA) is a document reporting the results of analytical testing on a specific peptide batch, including purity (HPLC), identity (mass spectrometry), endotoxin levels, and other quality metrics.
For research-grade peptides, the standard threshold is greater than or equal to 98% HPLC purity. Below 95%, impurity profiles can confound experimental results. Purity is the single most important number on a COA.
Red flags include: no batch/lot number, no HPLC chromatogram (just a number), suspiciously perfect purity (99.99%), no mass spectrometry data, identical formatting across all products, and no option for third-party verification.
HPLC measures purity -- the percentage of correct peptide vs impurities. Mass spectrometry confirms identity -- whether the molecular weight matches the expected peptide sequence. Both are needed: HPLC without MS tells you something is pure but not what it is.
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