How to read a certificate of analysis (CoA)
How to read a peptide certificate of analysis: lot numbers, mass spectrometry identity, HPLC purity, net peptide content and the warning signs of an unreliable CoA.
A certificate of analysis (CoA) is the laboratory report for a specific batch of a product. For research peptides it is the main evidence that the vial contains the right molecule at the stated purity. Knowing how to read one takes a few minutes and protects your results.
1. Batch details
Check that the product name, lot or batch number and quantity on the CoA match the label on your vial. A CoA for a different lot tells you nothing about the material you have. Look for a test date, and the name of the laboratory that carried out the analysis.
2. Identity: mass spectrometry (MS)
Mass spectrometry confirms that the molecule is the one claimed. The CoA should show the theoretical molecular weight from the sequence and the observed mass. They should agree closely, typically within about 1 Da for small peptides. Electrospray results often appear as several charge states (for example [M+2H]²⁺, [M+3H]³⁺); each should correspond to the same parent mass.
3. Purity: HPLC
Reverse-phase HPLC separates the target peptide from related impurities such as truncated or deleted sequences. Purity is reported as the main peak’s percentage of total peak area, usually measured by UV at 214–220 nm.
- A good CoA includes the chromatogram itself, not just a number.
- Look for one dominant peak with small, well-separated minor peaks.
- Research-grade peptides are commonly specified at ≥98% or ≥99% HPLC purity.
4. Purity is not the same as peptide content
HPLC purity tells you what fraction of the peptide material is the correct sequence. It does not tell you how much of the powder’s weight is peptide. Lyophilised peptides also contain counter-ions (often trifluoroacetate or acetate) and residual water, so net peptide content is commonly 70–90% of the weighed mass. If a CoA reports peptide content, typically measured by nitrogen analysis or amino acid analysis, use it when calculating concentrations.
5. Other tests you may see
- Appearance: usually “white to off-white lyophilised powder”. Copper peptides such as GHK-Cu are blue.
- Water content: by Karl Fischer titration.
- Counter-ion content: for example residual TFA.
- Endotoxin (LAL) and sterility: relevant mainly to cell-culture work.
Warning signs
- No lot number, or a lot number that doesn’t match the vial.
- A purity figure with no chromatogram, or a chromatogram with no axis labels or scale.
- Identical certificates reused across different products or batches.
- No laboratory name, no date, or signs of editing in the document.
- Implausibly round results, such as 100.00% purity.
If in doubt, ask the supplier which laboratory performed the test, and contact that laboratory to confirm the report is genuine. Independent laboratories accredited to ISO/IEC 17025 are the most reliable source of analysis.
All Peptide Pro products are supplied for laboratory and in-vitro research only. They are not medicines and are not for human or veterinary use.