How to Read a Peptide Certificate of Analysis (COA)
Learn how to read and verify a peptide Certificate of Analysis — purity percentage, HPLC chromatogram, mass spectrometry, and red flags to watch for.
Overview
A Certificate of Analysis (COA) is the primary quality document for research peptides. It verifies purity, identity, and absence of contaminants. Understanding how to read a COA is essential for sourcing safe, effective peptides. This guide covers the key sections and red flags.
What You Need
- Peptide COA (PDF from vendor)
- Basic understanding of HPLC and mass spectrometry (explained below)
Step-by-Step Instructions
Check the purity percentage
The purity percentage (e.g., '>98% purity') indicates what fraction of the sample is the target peptide. Research-grade peptides should be ≥95% pure. Pharmaceutical-grade is ≥99%. Anything below 90% is substandard.
Examine the HPLC chromatogram
The HPLC chromatogram shows peaks representing different compounds in the sample. A high-purity peptide has one dominant peak (the peptide) with small or absent secondary peaks (impurities). The area under the main peak divided by total area = purity %.
Verify identity with mass spectrometry
Mass spectrometry (MS) confirms the molecular weight of the peptide matches the expected value. The COA should show the theoretical MW and the observed MW — they should match within 0.1 Da.
Check for endotoxin testing
Endotoxins (bacterial lipopolysaccharides) cause fever, inflammation, and sepsis. Injectable peptides should have endotoxin levels <1 EU/mg (European Pharmacopoeia standard). Look for LAL (Limulus Amebocyte Lysate) test results.
Verify the COA is from an independent lab
The most trustworthy COAs are from independent third-party labs (not the vendor's in-house lab). Look for lab name, accreditation (ISO 17025), and date of testing.
Common Mistakes to Avoid
Accepting purity claims without a chromatogram
Fix: Always request the HPLC chromatogram. A purity number without supporting data is unverifiable.
Ignoring the testing date
Fix: COAs older than 12 months may not reflect the current batch. Request a recent COA for the specific batch you are purchasing.
Not checking for MS confirmation
Fix: Purity alone does not confirm identity. A 98% pure sample could be 98% of the wrong peptide. Mass spectrometry is required to confirm identity.
Frequently Asked Questions
What purity should research peptides be?
Research-grade peptides should be ≥95% pure by HPLC. For injectable use, ≥98% is recommended. Pharmaceutical-grade (for human clinical use) requires ≥99%.
How do I know if a COA is fake?
Red flags: no lab name or accreditation, no HPLC chromatogram (just a number), no mass spectrometry data, MW does not match the expected value, or the lab cannot be found online. Cross-reference the lab with independent sources.
Do all peptide vendors provide COAs?
Reputable vendors provide COAs for every batch. If a vendor does not provide a COA on request, do not purchase from them. COA availability is a minimum quality standard.
Peptides Covered in This Guide
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