How to Read a Peptide Certificate of Analysis (COA)
Learn how to interpret HPLC chromatograms, mass spectrometry data, and purity percentages on a Certificate of Analysis. A guide for researchers evaluating peptide quality.
A Certificate of Analysis (COA) is the single most important document when evaluating the quality of a research peptide. It provides independently verified data about a compound's identity, purity, and quality — produced by a third-party laboratory, not the vendor.
Understanding how to read a COA is essential for any researcher working with synthetic peptides. A properly documented COA should contain several key data points that allow you to independently verify the compound you've received.
The first element to examine is the HPLC (High Performance Liquid Chromatography) data. HPLC separates the components of a sample and measures the relative abundance of the target compound versus impurities. A high-quality research peptide should show a purity of 95% or higher, with premium suppliers like Experts Only Research maintaining a minimum threshold of 99% across their entire catalog.
The HPLC chromatogram — a graph showing peaks at different retention times — should display a single dominant peak representing the target peptide. Any secondary peaks represent impurities, and their relative area indicates the percentage of contamination. Look for a clean chromatogram with minimal secondary peaks.
The second critical element is mass spectrometry (MS) data, specifically LC-MS/MS (Liquid Chromatography-Mass Spectrometry/Mass Spectrometry). While HPLC tells you how pure the sample is, mass spectrometry confirms what the compound actually is by measuring its molecular weight. The observed mass-to-charge ratio (m/z) should match the theoretical molecular weight of the target peptide within an acceptable margin (typically ±0.1%).
Key items to verify on any COA include the batch or lot number (confirming the COA matches your specific vial), the date of analysis (recent testing is preferable), the name and credentials of the testing laboratory, and the specific methods used (HPLC column type, mobile phase, gradient conditions).
Red flags to watch for include COAs without a named laboratory, documents showing only a purity number without chromatographic data, generic or template-style COAs that don't reference specific batches, and vendors who only provide COAs "upon request" rather than making them publicly available.
At Experts Only Research, every compound is tested by independent third-party laboratories including Analytical Sciences LLC and Janssen Reference Labs. Full COAs are available for download before purchase on each product page — because transparency drives trust.
Disclaimer: This article is for educational and informational purposes only. All products sold by Experts Only Research are strictly for in-vitro laboratory research purposes. Not intended for human or animal consumption. Not evaluated by the FDA.