How to read a peptide certificate of analysis

A certificate of analysis is the only document that connects a marketing claim like “≥99% purity” to a physical vial. Most vendors say they have one. Far fewer publish one you can check. Here is how to read the ones you’re shown.

The four things a real COA has

1. An independent laboratory, named. The header should identify who ran the test: a contract lab with its own address and report numbering, not the vendor’s brand. Janoshik (Czech Republic) is the lab most research vendors use; MZ-Biolabs, Chromatography Services and various university core facilities also appear. If the lab is the seller, the document is a product sheet, not a certificate.

2. A batch or lot number that matches your vial. A COA describes one synthesis run. It is meaningless for a different run, however similar. The lot on the report must match the lot printed on the vial label, and a vendor that ships unlabelled vials has nothing to match against.

3. An HPLC chromatogram with the purity figure derived from it. High-performance liquid chromatography separates the target peptide from everything else in the vial. You should see the trace itself: one dominant peak, with smaller peaks for truncated or deletion sequences. Purity is the main peak’s area as a percentage of total peak area. A number without the trace is a claim, not a measurement.

4. Mass spectrometry confirming identity. HPLC tells you how pure the material is. It doesn’t tell you what the material is. Mass spectrometry does: the report should give an observed molecular mass and the theoretical mass for the named peptide, and the two should agree within a fraction of a dalton. BPC-157’s monoisotopic mass is about 1419.5 Da; GHK-Cu’s copper complex is about 401.9 Da. A COA that skips MS could be describing a very pure vial of the wrong compound.

Things people mistake for quality signals

“Purity” is not “quantity”. A 5 mg vial at 99% purity may contain 3 mg of peptide. The rest is water and counter-ions such as trifluoroacetate left over from synthesis. The measurement that captures actual content is net peptide content or a quantitative assay against a reference standard. Few research vendors report it. When one does, it’s a meaningful sign.

Endotoxin and sterility are separate tests. HPLC and MS say nothing about bacterial contamination. A sterility or endotoxin (LAL) result is a different assay and is rarely included for research-grade material. Its absence isn’t damning, but it should not be assumed.

A COA on the website is not a COA for your vial. A single flagship report reused for years across every batch is the most common form of decoration. Ask for the report for the lot you received.

Five warning signs

1. No lab name, or a lab name that returns no results when you search it.
2. A purity figure with no chromatogram.
3. No mass spectrometry section.
4. The same report image on every product page, with the compound name changed.
5. A report dated years before the product’s launch, or with a lot number format that doesn’t match the vial.

What to do with one

Read the header, match the lot, look at the trace, check the mass. That takes two minutes and separates vendors who tested from vendors who typed. For material used in any serious research, a lab that publishes its reports per batch, with lot numbers you can match, is the only kind worth buying from.