Reading a Certificate of Analysis: Why COAs Matter
Peptide Basics
A Certificate of Analysis is the single most important document attached to a research peptide, and also one of the most commonly misunderstood. This article breaks down what a COA actually verifies and how to read one.
Quick summary
- A COA exists to answer one question: does this vial contain what the label says, at the purity it claims.
- Purity is typically reported from HPLC testing, expressed as a percentage of total peak area.
- The lot number on a COA must match the lot number on the vial, or the documentation does not apply.
- A COA is only as trustworthy as the lab that issued it — independent, third-party testing matters.
What a COA actually verifies
A Certificate of Analysis is a lab report confirming two things about a specific batch, or lot, of a compound: identity and purity. Identity confirms that the vial actually contains the peptide it claims to contain, rather than a different compound or an incomplete synthesis byproduct. Purity quantifies how much of the vial’s content is the target peptide, versus impurities, degradation products, or synthesis byproducts.
Reading the purity percentage
Purity is most commonly measured through HPLC, high-performance liquid chromatography, a technique that separates a sample’s components and measures how much of the total signal corresponds to the target peptide. A result reported as 99% purity means that roughly 99% of the measured peak area in the chromatogram corresponds to the intended compound, with the remainder attributed to impurities or related byproducts.
It is worth understanding that HPLC purity is a relative measurement based on detectable peak area, not an absolute guarantee of zero contamination. This is one reason identity testing, typically through mass spectrometry, is used alongside HPLC purity testing rather than as a replacement for it.
Why the lot number matters
A COA is only valid for the specific lot it was tested against. Manufacturing occurs in discrete batches, and even small variations between batches can affect purity. The lot number printed on your vial should match the lot number on the COA you are referencing; if they do not match, that documentation does not actually verify what is in your vial.
This is also why logging lot numbers alongside experimental data is considered good research practice. If an unexpected result occurs, having the lot number on record makes it possible to trace the result back to a specific, verifiable batch rather than an assumption about product quality.
Why the testing lab matters
A COA is only as credible as the lab that produced it. Independent, third-party labs with no financial stake in the outcome carry more weight than in-house testing, since there is no incentive to inflate results. A trustworthy COA should include the testing lab’s name, a specific test date, and a specific lot number, rather than a generic document with none of these details.
Frequently asked questions
Does a high purity percentage guarantee a peptide is safe?
Purity confirms how much of the sample is the intended compound, at the time of testing. It does not by itself address storage after purchase, handling, or any other variable that occurs after the COA was issued.
What is the difference between identity and purity testing?
Identity testing confirms the vial contains the correct compound. Purity testing quantifies how much of the sample is that compound versus impurities. Both are typically needed for a complete picture.
Where can I find the COA for my order?
You can look up any lot number directly on our site to view the corresponding Certificate of Analysis.
Look up your lot Certificate of Analysis →
For laboratory and research use only. Not for human consumption. This article is for informational purposes; it is not medical advice.
