How to read a Certificate of Analysis

A certificate of analysis, or COA, is the lab report that tells you what is actually inside a vial. For research peptides it is the single most important document a supplier can give you, because purity and identity cannot be judged by looking at a lyophilized powder. This guide walks through what a real COA proves, how to read the two results that matter, and how to confirm the certificate belongs to the exact lot you received.

The basics

What a certificate of analysis actually proves

A useful COA answers two separate questions. First, identity: is this molecule the peptide the label claims? Second, purity: what fraction of the material is that peptide, versus water, salts, and synthesis byproducts? A vendor can print a purity number on a label without ever testing it. A COA from a third-party lab, tied to a specific batch, is the evidence behind the number.

Two analytical methods carry most of that weight. Mass spectrometry confirms identity by measuring the molecular weight. Reverse-phase HPLC measures purity by separating the sample into its components and reporting how much of the signal belongs to the target peptide.

Purity

Reading the HPLC purity result

HPLC pushes the dissolved sample through a column so its components come out at different times. A detector plots those components as peaks. The target peptide is the large, dominant peak, and purity is reported as the area of that peak divided by the area of everything detected, usually shown as a percentage such as 99.2 percent.

• Look for a single tall, clean peak with a flat baseline around it. A dominant peak with only tiny neighbors is what high purity looks like.
• Check the number against the claim. If the label says at least 99 percent and the chromatogram reports 99.2, they agree.
• Be cautious of clusters of large secondary peaks, a noisy baseline, or a purity figure with no chromatogram image to back it up.

Identity

Reading the mass spectrometry result

Mass spec confirms you have the right molecule, not merely a pure one. The report lists an observed mass and compares it to the expected mass for that peptide. When the observed value matches the theoretical molecular weight, identity is confirmed. A pure sample of the wrong compound is still the wrong compound, which is why identity and purity are always reported together.

Verification

How to confirm the COA belongs to your vial

This is the step most buyers skip and the one that matters most. A certificate only means something if it describes the batch in your hand. Every RTT vial is printed with a lot number, and that lot number matches a dated certificate on file. Read the lot from your vial, look it up, and confirm the compound, the mass, the purity, and the test date all line up.

• Match the lot number on the vial to the lot on the certificate. They must be identical.
• Confirm the compound and molecular weight match the product you ordered.
• Check that the certificate is dated and names the method, not just a bare percentage.

Red flags

Warning signs to walk away from

• No COA at all, or one available only after you ask several times.
• A generic certificate reused across every product, with no lot number and no date.
• A purity figure with no chromatogram or mass spec to support it.
• A lot number on the paper that does not match the number printed on the vial.