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How to read a peptide certificate of analysis

Quality2 min read

A certificate of analysis (COA) is the most useful document a peptide supplier can give you, and the easiest to fake. A single line that says “Purity: 99.2%” tells you very little. A complete report tells you what was tested, how, by whom, and on which batch. Here’s how to read one.

1. Check the batch number first

The report must name the batch it applies to, and that number must match the one on your vial and packing slip. A COA with no batch number, or a number that doesn’t match, says nothing about the material in your hands.

2. Find out who did the testing

Look for the name of the laboratory, the analysis date and, ideally, the analyst or approver. Reports produced only by the manufacturer are useful but not independent. Third-party reports are stronger evidence, especially when you can contact the lab to confirm them.

3. Read the HPLC chromatogram, not just the number

Reverse-phase HPLC separates the target peptide from impurities such as truncated or deletion sequences. Purity is the area of the main peak as a percentage of all integrated peaks. When reading the trace:

  • Look for one dominant peak with a clean baseline either side.
  • Check the integration table. It should list every peak with its retention time and area, and the percentages should add up.
  • Note the detection wavelength, usually 214–220 nm, where the peptide bond absorbs.
  • Be wary of perfect numbers with no trace attached, or a trace that looks identical across different products.

4. Confirm identity with the mass spectrum

HPLC shows how pure a sample is, but not what it is. Mass spectrometry, usually electrospray ionisation (ESI-MS), confirms the molecular weight. Compare the observed mass with the theoretical mass for the sequence, including any modifications such as acetylation, amidation or disulfide bonds. Larger peptides appear as several multiply charged ions; the report should show the deconvoluted mass or explain the charge states.

5. Know what the report doesn’t cover

A standard COA doesn’t measure everything. Unless stated, it won’t include net peptide content, counter-ion content, water content, endotoxin levels or sterility. If your experiment depends on any of these, ask for them specifically. We explain the difference between purity and peptide content in a separate article.

A quick checklist

  1. Batch number matches your vial.
  2. Testing lab, date and method are named.
  3. Full HPLC trace with an integration table is included.
  4. Observed mass matches the theoretical mass.
  5. Specification and result are both shown, so you can see the pass criteria.

Every RoyalPep batch report is published on our Lab Reports page against its batch number.