How to read a certificate of analysis

Every peptide supplier claims 99% purity. The certificate of analysis (COA) is where that claim is either proven or not. This guide walks through a COA section by section, so you know what a complete one looks like and what should make you ask questions.

What a COA is

A certificate of analysis is a quality-control document for one specific lot. It reports the analytical tests run on a sample from that lot and their results.

A legitimate COA is lot-specific. It carries a lot number that matches the product it describes. A generic document that applies to "all lots", or has no lot number, doesn't tell you anything about the vial in front of you.

A COA should answer five questions:

• Identity: is this the compound the label says?
• Purity: how much of the sample is the target compound?
• Content: how much peptide is actually in the vial, compared with the label?
• Method: how was it tested, and were the results measured against stated specifications?
• Traceability: which lot was tested, and when?

The header

• Compound: the product tested, often with its CAS number, molecular formula and molecular weight.
• Lot number: the unique identifier for this production run, printed on the vial label. If it's missing, the document can't be tied to your product.
• Report number and sample ID: identifiers for this particular analysis.
• Dates: when the sample was received, when it was analyzed and when the report was issued.

Appearance and molecular information

Most peptides are described as a lyophilized (freeze-dried) powder, usually white to off-white. The COA may also list the total mass of the sample, the molecular formula, the expected molecular weight in daltons and the CAS number. Together these define exactly which compound was being tested for.

Chromatographic purity: the core number

Liquid chromatography separates a sample into its components. The classic method is high-performance liquid chromatography (HPLC); many labs now couple the chromatography directly to a mass spectrometer (LC-MS or LC-MS/MS). Either way, the result is a chromatogram, a graph with a peak for each substance detected.

• One dominant peak at the expected retention time is the target compound.
• Peak area percentage is the purity figure: the share of detected material that is the target.
• Minor peaks are impurities. They should be small.

Questions to ask: is the chromatogram image included, or just a number? Is the main peak sharp, or broad and shouldered? Several peaks of similar height mean low purity.

Mass spectrometry: confirming identity

Chromatography tells you how pure a sample is. Mass spectrometry (MS) tells you what it is, by measuring molecular mass. The observed mass should match the theoretical mass of the target compound closely. A sample can be 99% pure and still be the wrong compound, so MS is the identity check that chromatography alone can't provide.

In liquid chromatography–tandem mass spectrometry (LC-MS/MS), identity and purity come from the same run. The report typically lists the precursor ion (the intact molecule's mass-to-charge ratio) and the MRM transitions, which are specific fragments the instrument watches for. A good report also states the instrument, column and solvents used.

Net peptide content and label accuracy

Purity is a ratio: how much of the detected material is the target. It doesn't tell you how much peptide is in the vial. Two further results cover that:

• Net peptide content is the share of the powder's weight that is the peptide itself, as opposed to counter-ions and residual water. It is always below 100%. Our article on peptide purity explains why.
• Label accuracy compares the amount of peptide measured with the amount stated on the label, as a percentage.

Results against specifications

Each result should sit next to the specification it was measured against, for example chromatographic purity "≥98%" with the measured figure and a pass or fail status. A number with nothing to compare it to is harder to judge.

Other tests you may see

• Amino acid analysis confirms the amino acid composition matches the expected sequence.
• Endotoxin testing (usually the LAL method) measures bacterial endotoxin, which can interfere with cell-based experiments. Results should be a number with units, not just "pass".
• Heavy metals and sterility are part of fuller panels some labs offer.

Not every COA includes every test. What matters is that the COA says clearly which tests were run, how, on which lot and when.

Signs a COA deserves a second look

• No lot number, or one that doesn't match the vial
• No test dates or report number
• The same document reused across products or dates
• Only round numbers, or no chromatogram
• Results with no specification to compare them against
• Purity reported with no identity test at all

How we publish ours

Every lot we sell is tested by an independent laboratory before it goes on sale. The full report is shown on each product page under a "View COA" button. It carries the lot number printed on your vial, a report number, and the dates the sample was received and analyzed. Testing is by liquid chromatography–tandem mass spectrometry (LC-MS/MS), which confirms identity and measures chromatographic purity in one run, alongside net peptide content and label accuracy. Each result is shown against its specification, with the method details and the chromatogram. Match its lot number to the label on your vial.

All products are sold for laboratory research use only and are not for human or veterinary use.