How to Read a Peptide Certificate of Analysis (COA)
A Certificate of Analysis (COA) is the single most important document you should request from any peptide vendor. It provides analytical evidence that the peptide you received matches what was ordered in terms of identity, purity, and quality. Yet many researchers either skip reviewing COAs entirely or don't fully understand the data presented. This guide walks through every section of a standard peptide COA.
What Is a COA?
A COA is a quality control document issued by the manufacturer or an independent testing laboratory. It summarizes the results of analytical tests performed on a specific batch of a product. For research peptides, a COA typically includes results from High-Performance Liquid Chromatography (HPLC) and Mass Spectrometry (MS), along with general product information.
Key Sections of a Peptide COA
1. Product Information
This section lists the peptide name, catalog number, batch/lot number, molecular formula, theoretical molecular weight, and quantity. Always cross-reference the batch number on the COA with the batch number on your product vial. If they don't match, the COA may not apply to your specific product.
2. HPLC Purity Data
HPLC (High-Performance Liquid Chromatography) is the gold standard for peptide purity assessment. The COA should report the purity percentage, typically as a percentage of the total peak area on the chromatogram. Research-grade peptides should show 95%+ purity, while premium vendors often guarantee 99%+ purity.
Look for the actual chromatogram if provided. The main peak should be tall and sharp with minimal smaller peaks (which represent impurities, truncated sequences, or degradation products). The retention time should be consistent with the expected hydrophobicity of the peptide.
3. Mass Spectrometry Data
Mass spectrometry confirms the molecular identity of the peptide. The observed molecular weight should match the theoretical molecular weight within the instrument's margin of error (typically within 0.1-0.5 Da for ESI-MS). This tells you that the peptide has the correct amino acid sequence and molecular structure.
If the observed mass is significantly different from the theoretical mass, this could indicate synthesis errors, amino acid deletions, or the wrong peptide entirely.
4. Appearance and Solubility
Most lyophilized peptides should appear as a white to off-white powder. The COA may also include solubility data, indicating which solvents were tested and at what concentrations the peptide dissolves.
5. Amino Acid Analysis (If Included)
Some premium COAs include amino acid analysis, which quantifies the ratio of each amino acid in the peptide. This provides additional confirmation that the sequence was synthesized correctly.
Red Flags to Watch For
Third-Party vs. In-House Testing
In-house COAs are generated by the vendor themselves. While not inherently unreliable, they lack the independence of third-party testing. The gold standard is a COA from an accredited independent laboratory, as this eliminates potential conflicts of interest.
Top vendors like MedgePeptides provide third-party COAs for every batch, giving researchers confidence in the analytical data's objectivity and accuracy.
Conclusion
Reading a COA is an essential skill for any researcher working with synthetic peptides. By understanding what each section represents and knowing what red flags to look for, you can make informed decisions about product quality and vendor reliability. Always request and review the COA before beginning any research protocol.