How to read a peptide certificate of analysis

What is a peptide certificate of analysis?

A certificate of analysis, or COA, is a report from a laboratory describing what it found when it analysed a specific sample. For a peptide vial that usually means what the molecule is, how pure it is and how much of it there is.

The key word is specific. A COA is evidence about one sample from one batch, analysed on one date. It is not a general quality stamp for a product name, and it says nothing about batches made before or after.

What should a peptide COA include?

Before reading any numbers, check that the document identifies itself properly. A complete certificate shows:

• The name of the laboratory that ran the analysis, and how to contact it.
• A description of the sample as received, including the label claim in milligrams.
• A batch or lot code that you can match to the code on your vial.
• The date the sample was received and the date it was analysed.
• The method behind each result, such as LC-MS for identity and HPLC with UV detection for purity.
• Results with units, and the expected value where one applies.
• The name and signature of the person who approved the report.
• A way to verify the report with the laboratory, such as a task number and key.

If the batch is missing, or does not match your vial, stop there. The rest of the certificate may be accurate, but it describes a different sample.

How do I read the identity result?

Identity is usually shown as a mass from mass spectrometry. The report should list the mass it expected for the named peptide and the mass it observed. For tirzepatide the average molecular weight is about 4813.5 g/mol, so an identity result should land close to that once any charge states are accounted for.

Large peptides often appear in the spectrum carrying several charges, so the raw peak can sit at a fraction of the full mass. In one published analysis, semaglutide was identified at 1029.3 Da as an ion carrying four charges (Ashraf et al., 2024). A good report explains this or converts the value back to the full mass. A bare "identity: conforms" with no masses is weaker, because you cannot check it.

Mass spectrometry is the standard tool here. A peer-reviewed paper on peptide reference standards notes it "is often used to determine the monoisotopic mass of a peptide and to provide confirmation of the amino acid sequence" (McCarthy et al., Pharmaceutical Research, 2023). The identity lesson covers it in more depth.

How do I read the purity result?

Purity is usually a percentage from HPLC. It is the share of the main peak among all the peaks the detector saw, often measured by UV absorbance around 220 nm. A figure like 99.1% means the main peak made up 99.1% of the detected peak area.

Purity does not tell you the molecule is correct, and it does not tell you how many milligrams are in the vial. Water and counterions such as trifluoroacetate are largely invisible to a UV detector. In a study of synthetic glucagon, HPLC with UV detection gave a purity above 970 mg/g, while a full mass balance gave 896.36 mg/g once water and trifluoroacetic acid were counted (Wang et al., Scientific Reports, 2020). Purity: what HPLC measures goes further.

How do I read the amount or content result?

This is the line many certificates leave out. An amount result, sometimes called assay or quantity, measures the milligrams of peptide in the vial against a reference standard and compares that with the label. It should appear as a measured figure in mg next to the label claim, or as a percentage of the label.

A vial can be pure and still underfilled. If your certificate shows purity only, it has not answered whether the vial holds what the label says. See amount vs label for how this is measured.

How do I read an endotoxin result?

Endotoxin is a separate test for bacterial contamination, usually reported in endotoxin units per milligram (EU/mg). The common methods are described in USP Chapter 85, which the US FDA's guidance on endotoxin testing refers to (FDA, Pyrogen and Endotoxins Testing). An endotoxin result says nothing about identity, purity or amount, and a report that covers endotoxin only should say so plainly.

Who is allowed to sign a COA in the Philippines?

Under the Chemistry Profession Act, performing and certifying a chemical analysis are part of the practice of chemistry, and a document related to that practice is not considered official unless it is signed by a registered chemist with the chemist's registration number (RA 10657, Sections 4 and 40). A certificate issued abroad follows the rules of that country, but for a report produced locally, look for the chemist's name and registration number.

What are the warning signs on a certificate?

• No batch code, or a batch code that does not match your vial.
• A purity figure with no chromatogram, method or date.
• Identity stated as "conforms" with no expected or observed mass.
• No amount result, so the label claim was never checked.
• No laboratory name, or a laboratory you cannot contact.
• No signature, and no way to verify the report with the issuer.
• The same certificate used for several products, sizes or years.

None of these alone proves a vial is bad. They mean the certificate cannot carry the weight a seller is putting on it. The COA checker steps through these questions for a certificate you already have, and peptide seller red flags covers the wider picture.

How do I check the certificate is genuine?

Use the issuing laboratory's own verification route, not a link or screenshot from the seller. Many laboratories give each report a reference you can enter on their website. For one widely used example, see how to verify a Janoshik report.

Tested.ph records work the same way. Each record carries a task number and a key, for example 1042-K7QX9M, which anyone can check at tested.ph/verify. Analysis is done by a partner laboratory, and the report is signed by its registered chemist. The partner laboratory will be named before testing opens. To order a test on your own batch, start at the tirzepatide test page, and read the methods page for how each result is produced.