When you order a research peptide, you’re trusting that what’s in the vial matches what’s on the label. A Certificate of Analysis — COA — is how that trust gets verified. It’s the analytical document that proves a peptide was tested, what the results showed, and whether the compound meets research-grade standards. This guide explains what a COA contains, how purity is actually measured, what the numbers mean, and what to look for when evaluating whether a supplier’s documentation is legitimate.
Research Use Educational Framework
- Educational reference content only
- Analytical awareness concepts
- Research methodology considerations
- Non-clinical research context
What Is a COA?
A Certificate of Analysis is a document issued by a laboratory that records the results of analytical testing performed on a specific batch of compound. For research peptides, a COA typically includes the compound name, batch number, molecular weight, purity percentage, and the testing methods used to generate those results.
A COA is batch-specific — it documents the results for that particular production run, not the compound in general. This matters because purity can vary between batches. A reputable supplier provides a unique COA for every batch they produce, and makes those documents accessible to customers before or at the time of purchase. If a supplier provides a single generic COA for a compound rather than batch-specific documentation, that’s a red flag worth noting.
How Purity Is Measured — HPLC Explained
The most common method for measuring peptide purity is High-Performance Liquid Chromatography, or HPLC. The process works by pushing a dissolved peptide sample through a column packed with fine particles. Different components in the sample travel through the column at different speeds depending on their chemical properties — the target peptide arrives at one time, impurities at others.
A detector at the end of the column measures the signal as each component passes through, producing a graph called a chromatogram. The area under each peak represents the relative quantity of that component. Purity is calculated as the percentage of the total peak area that belongs to the target peptide. A result of 98% purity means 98% of the detected signal came from the intended compound — the remaining 2% came from synthesis byproducts or other impurities.
How to Read a Chromatogram
A chromatogram looks like a graph with one or more peaks rising from a flat baseline. For a high-purity peptide, you want to see one dominant peak — tall, sharp, and well-separated from any other peaks. That dominant peak is your peptide. Any additional smaller peaks represent impurities.
The x-axis shows retention time — how long it took each component to travel through the column. The y-axis shows signal intensity. The area under each peak is what gets used to calculate purity percentage. A clean chromatogram with a single dominant peak and minimal background noise indicates a well-synthesized, well-purified compound. Multiple significant peaks, a broad main peak, or a messy baseline are signs of lower purity or synthesis issues.
Mass Spectrometry — Confirming Identity
HPLC tells you how pure a compound is. Mass Spectrometry — MS — tells you what it actually is. Mass spectrometry measures the molecular weight of the compound in a sample and compares it to the theoretical molecular weight of the target peptide.
If the measured mass matches the expected mass, it confirms the compound has the correct molecular identity — not just that something pure is present, but that the right thing is present. The best COAs include both HPLC purity data and mass spectrometry confirmation. HPLC alone can show high purity but can’t prove identity. MS alone confirms identity but doesn’t measure purity. Together they give a complete picture. When evaluating a supplier, look for COAs that include both — it’s the gold standard for research-grade documentation.
What Purity Percentages Actually Mean
Research-grade peptides are typically sold at 98%+ purity. Some suppliers offer 95% as a standard grade. The difference matters more than it might seem. In a research setting, impurities aren’t inert — they’re unknown compounds that can interact with biological systems in ways that introduce variables into experimental results.
A 95% pure peptide contains 5% unknown material by weight. For some research applications that’s acceptable. For receptor binding studies, cell-based assays, or any experiment where compound behavior needs to be precise and reproducible, higher purity is strongly preferable. When comparing suppliers, purity percentage is one of the most direct indicators of compound quality — and it should always be backed by actual HPLC data, not just a stated claim on a product page. BioStrata publishes batch-specific COAs for all compounds in our COA Library.
Red Flags and What Good Documentation Looks Like
Not all COAs are equal. Some suppliers publish legitimate third-party tested documentation. Others publish internal documents with no way to verify the testing was performed independently. Knowing what good looks like helps you evaluate what you’re actually getting.
Good COA documentation includes: a specific batch number, the date testing was performed, the testing method used (HPLC, MS), the actual chromatogram image — not just a number, the purity result expressed as a percentage, and the molecular weight confirmed by mass spectrometry. Red flags include: no chromatogram image, no batch number, no testing date, purity claims without methodology, or a single COA applied to all batches of a compound. Transparency in documentation is one of the clearest signals of a supplier’s quality standards. For guidance on evaluating suppliers more broadly, see How to Evaluate Peptide Vendors.
- CONTINUE LEARNING
Explore Related Peptide Topics
Continue building your understanding by exploring related foundational peptide topics.