How do you read a peptide certificate of analysis (COA)?

What is a certificate of analysis for a peptide?

A certificate of analysis (COA) is a laboratory report that describes the testing of one sample from one lot. It is evidence about that lot only, not about a product line or a brand.

A useful COA lets you trace the report back to a physical vial. A report that cannot be tied to a lot tells you very little, however good the numbers look.

What should be on a peptide COA?

At minimum: a sample identifier, a lot or batch number, the name of the laboratory, the test date, the methods used, and the results. Most buyers want to see these results in separate lines.

Certificates in our library show the sample number, the lot, the method used, the purity, whether identity was confirmed, and the measured content.

How do you read an HPLC purity result and chromatogram?

HPLC purity is the main peak's share of the total peak area, shown as a percentage. It tells you how much of what the detector saw is the target peptide.

Look at the chromatogram itself, not only the number. You want one dominant peak, a flat baseline, and any smaller peaks small and separate. The report should state the detection wavelength (peptides are commonly read at 214 or 220 nm, where the peptide bond absorbs) and the column and gradient used.

Two cautions. First, purity by peak area ignores anything the detector does not see, such as water and salts. Second, a very high figure depends on how the lab drew the baseline and set integration, so a chromatogram should be attached. See peptide purity vs content.

What does the mass spectrometry result tell you about identity?

Mass spectrometry measures the mass of the molecules in the sample. If the observed mass matches the expected mass for the peptide, within the instrument's stated tolerance, the sample is consistent with the right molecule.

A good report shows the expected mass, the observed mass and the difference. A line that only says "conforms" gives you nothing to check. Peptides often appear at several charge states, so the report may show a raw spectrum plus a deconvoluted mass. Both are fine. Missing numbers are not.

Identity and purity are separate questions. A full comparison is in HPLC vs mass spectrometry.

What does a COA not tell you?

A COA tells you what was measured on the sample the lab received. It does not tell you the whole story about the lot or the vial.

• Amount. HPLC purity is not the milligrams in the vial. Only a content result answers that.
• Contaminants. Endotoxin and heavy metals need their own panels. If a report does not list them, they were not tested.
• Other vials. The sample is one vial. It supports the lot only if sampling and lot control are sound.
• Age. A report is a snapshot. Check the test date against the lot.

Ask what was tested and what was not. A supplier who cannot answer clearly is telling you something.

Why a COA that arrives late or generic is a sourcing problem

Many buyers meet the same problem: one PDF for a whole product range, a report with no lot, or paperwork that appears only after payment. None of these lets you evaluate a lot before you commit.

We publish certificates in a public library with their sample number and lot, and a certificate issued in your company's name is available with a wholesale order.

How do you check that the COA matches the vial in your hand?

Compare four things: the lot number, the product name, the test date and the lab name. All four should be on both the report and your paperwork, and the lot should match what is printed on the vial.

If the report is hosted online, open it from the supplier's own page or label link and confirm it shows the same sample identifier. A PDF forwarded by email is easier to alter or reuse than a report hosted at an address the supplier controls, though neither proves authenticity alone. If you want to confirm a report, ask the lab named on it.

What are the red flags on a peptide COA?

These are warning signs, not proof of a problem. Each is a reason to ask a question before you buy.

• No chromatogram or spectrum, only a summary line
• No lot number, or a lot that does not match the vial
• The same report used for different products
• An unnamed lab, or a lab owned by the seller
• A purity of exactly 100.0%, with no integration detail
• A content line missing, or "conforms" with no numbers
• A report available only after payment

Where can you see a real example?

Read one end to end. Pick a certificate, find the lot, the lab and the date, then read the chromatogram and the mass result before you read the purity percentage.

You can read published certificates in our certificate library.