How to Read a Peptide Certificate of Analysis
A practical guide to understanding HPLC chromatograms, mass spec data, and purity percentages on vendor-issued CoAs.
Dr. Elena Marsh
Chief Science Officer
What Is a CoA?
A Certificate of Analysis (CoA) is a document issued by a manufacturer or third-party laboratory that confirms the identity, purity, and quality of a peptide product. Every reputable vendor should provide a CoA for each batch they sell.
Key Sections to Review
1. Peptide Identity
The CoA should list the peptide's full name, sequence, molecular weight, and CAS number (if applicable). Cross-reference the stated molecular weight against known databases like PubChem or UniProt.
Red flag: If the molecular weight doesn't match the expected value for the peptide sequence, the product may be mislabeled or contaminated.
2. HPLC Purity
High-Performance Liquid Chromatography (HPLC) is the gold standard for measuring peptide purity. Look for:
- •Purity percentage — 95% or above is acceptable for research; 98%+ is preferred
- •Chromatogram — a clean, single dominant peak indicates high purity
- •Retention time — should be consistent with the expected value for that peptide
- •Column and method details — C18 columns with acetonitrile/water gradient are standard
3. Mass Spectrometry
Mass spec (MS) confirms the molecular identity. The observed mass should match the theoretical mass within ±1 Da. MALDI-TOF and ESI-MS are the most common methods.
4. Additional Tests
Some CoAs include:
- •Amino acid analysis — confirms the sequence composition
- •Endotoxin testing — critical for injectable peptides
- •Sterility testing — ensures no microbial contamination
- •Water content (Karl Fischer) — important for lyophilized peptides
How PepAssure Verifies CoAs
Our automated pipeline cross-references vendor-submitted CoAs against:
1. Expected molecular weights for the stated peptide
2. Historical HPLC profiles from our database
3. Known lab formatting standards
4. Batch consistency across multiple orders
We flag discrepancies and assign a CoA Verification score as part of the PVS scoring system.
Quick Checklist
- •✅ Peptide name and sequence match the product listing
- •✅ Purity ≥ 95% (preferably ≥ 98%)
- •✅ Mass spec confirms molecular weight (±1 Da)
- •✅ Chromatogram shows a single dominant peak
- •✅ Lab name and date are present on the document
- •✅ Batch number matches your order
- •❌ Blurry or clearly edited documents
- •❌ Missing lab details or dates
- •❌ Purity claims without supporting chromatogram