Understanding Purity & COA Reports
A Certificate of Analysis (COA) is the most important document accompanying any research peptide. Knowing how to read one is essential for evaluating quality, choosing reliable suppliers, and producing reproducible results.
What HPLC purity means
High-Performance Liquid Chromatography (HPLC) separates the components of a sample by passing it through a column under high pressure. Each component elutes at a characteristic time, producing a chromatogram with peaks proportional to concentration. A 99% HPLC purity result means 99% of the area under the curve corresponds to the target peptide; the remaining 1% represents minor synthesis byproducts, truncated sequences, or related impurities.
Reading an HPLC chromatogram
A clean chromatogram shows one dominant peak with a retention time matching the expected target, and minimal noise across the rest of the trace. Multiple closely spaced peaks may indicate isomers or deletion sequences. Wide or trailing peaks can signal column issues or sample heterogeneity. The percentage figure on the COA is calculated by integrating the area of the main peak relative to the total integrated area.
Mass spectrometry confirmation
HPLC tells you how pure a sample is, but not what it contains. Mass spectrometry (MS) measures the molecular weight of each species in the sample, confirming that the main peak matches the theoretical mass of the intended peptide. A complete COA includes both an HPLC chromatogram and an MS spectrum — together they verify both purity and identity.
What to look for on a COA
A complete COA should be specific, dated, and traceable to a single batch of material. Vague or generic certificates that look identical across products are a red flag.
- Compound name and full chemical sequence
- Lot or batch number for traceability
- Net peptide content and HPLC purity percentage
- Mass spectrometry verification of identity
- Molecular weight and molecular formula
- Date of analysis and analyst or lab signature
- Endotoxin and sterility results when applicable
Net peptide content vs. mass purity
Lyophilized peptides often contain residual counter-ions, water, and salts from the synthesis process, which add weight without contributing active compound. Net peptide content — usually determined by amino acid analysis or nitrogen analysis — tells you how much of the labeled mass is actually peptide. A vial labeled '5 mg' at 80% net peptide content delivers 4 mg of usable material.
Why independent third-party testing matters
Independent testing prevents conflicts of interest. When a peptide is verified by an outside lab in addition to the manufacturer, the buyer has stronger assurance that the published results reflect the actual product in the vial — not a stock COA from a different batch. Look for suppliers who post third-party reports for each lot, with the lot number on the report matching the one on your vial.
Red flags to avoid
Be skeptical of suppliers who refuse to share COAs, post the same generic certificate for every product, or list purity figures without a chromatogram to back them up. A trustworthy supplier treats the COA as a routine deliverable, not a special request.