Lab notes · Quality
Peptide Purity 101: How to Read a Certificate of Analysis
A Certificate of Analysis is the single most important document in research-grade peptides. Here is how to read one with confidence.
Why the Certificate of Analysis exists
A Certificate of Analysis, or COA, is the document that tells you exactly what is inside a vial. It is batch-specific, meaning it belongs to one lot and no other, and it is the closest thing a peptide product has to a paper trail. Anyone can claim their peptides are pure. The COA is where that claim becomes checkable. At Amino Arsenal, every batch ships with quality documentation, and it is the first thing we point new customers toward.
Start with purity: HPLC
The purity figure on a COA usually comes from high-performance liquid chromatography, or HPLC. The technique separates the contents of the vial by size and charge, and the report shows what percentage of what is detected is the peptide you ordered. In research-grade peptides, 95% is generally the minimum acceptable figure, and 98% or higher is the standard researchers look for. Below 95%, the sample likely contains significant impurities that can confound experiments. Purity is the first number to check, and it should always be stated plainly, never hidden.
Then confirm identity: mass spectrometry
Purity tells you how much of the sample is one substance. Identity tells you that the substance is the right one. Mass spectrometry measures the mass of the peptides in the sample and compares it with the theoretical mass of the sequence it is supposed to be. When observed and theoretical masses match, the identity is confirmed. A COA that reports purity without identity data is incomplete, and a COA that reports neither is a red flag dressed in official-looking letterhead.
Lot numbers and dates matter
Traceability is the quiet half of quality. A proper COA carries a lot number, and that lot number should match the label on the vial you are holding. It also carries an analysis date, so you know how fresh the documentation is. If the numbers do not line up, or the dates are missing, treat the product with suspicion. Good vendors can tell you exactly which batch you have in your hand, because good vendors document every step.
What to do when numbers are missing
If a vendor cannot produce a batch-specific COA with HPLC purity, mass spectrometry identity, a lot number, and an analysis date, that is not a minor omission, it is a reason to walk away. Every Amino Arsenal batch is documented, and our certificates are available on request before you order. If you ever have a question about a figure on a COA, ask. A vendor who understands the science will be happy to explain it.
Sources
This note draws on published research and industry references. The direct links are listed so you can verify every claim yourself.
Knowledge, backed by product.
Every Amino Arsenal order ships with the same documentation standard we write about here.