How to read a peptide certificate of analysis (COA)
A certificate of analysis (COA) is the laboratory report for one specific production lot. It records which tests were run, by whom, and what they found. Reading one well takes a few minutes and tells you far more about a peptide than any product description.
1. Start with the identifying details
- Product name and sequence (or molecular formula), so you know exactly what was tested.
- Lot or batch number. This must match the lot number printed on your vial. A certificate for a different lot tells you nothing about the material in your hands.
- Test date and, where given, the manufacture date.
- The testing laboratory, with enough detail that it can be contacted.
2. Purity by HPLC
High-performance liquid chromatography (HPLC) separates the target peptide from impurities such as shortened or damaged sequences. A detector records each as a peak, and purity is the area of the main peak as a share of all the peaks, usually measured by UV absorbance at around 210 to 220 nm.
- Look for a percentage and the chromatogram itself: the graph of peaks. A single tall, sharp main peak with small side peaks is what a clean sample looks like.
- Research-grade peptides are commonly specified at 95% or 98% purity or higher. There is no single legal threshold for research material.
- HPLC purity only compares the peptide with other UV-visible material. Water and counter-ions do not show up, so high purity does not mean the vial is all peptide (see net peptide content below).
3. Identity by mass spectrometry
HPLC shows how pure the sample is; mass spectrometry (MS) shows that it is the right molecule. The certificate should list the theoretical molecular weight, calculated from the sequence, next to the observed value measured by the instrument.
- The two should agree closely. Small differences can come from instrument precision and from whether average or monoisotopic mass is reported.
- A large mismatch means the sample may be a different or modified sequence, whatever its purity.
- A mass spectrum attached to the certificate is stronger evidence than a single typed number.
4. Net peptide content
Freeze-dried peptide contains bound water and counter-ions (often trifluoroacetate or acetate from purification). Net peptide content is the share of the powder's weight that is actually peptide, typically measured by amino acid analysis or nitrogen analysis.
A peptide can be 99% pure by HPLC and still have a net peptide content well below 100%. If you need exact concentrations, this is the figure to use; our reconstitution math guide shows the correction. Many certificates do not report it, and that is worth knowing rather than assuming.
5. Other tests you may see
| Test | What it tells you |
|---|---|
| Endotoxin (LAL test) | Bacterial endotoxin, reported in EU/mg. Matters most for cell-based work, where endotoxin can trigger responses that look like results. |
| Water content (Karl Fischer) | How much of the powder is water. Feeds into net peptide content. |
| Counter-ion content | How much trifluoroacetate, acetate or chloride is present. Some assays are sensitive to trifluoroacetate. |
| Appearance and solubility | A basic check that the powder looks and dissolves as expected. |
| Quantity per vial | A measured amount of peptide in the vial, which confirms the fill rather than only the purity. |
Red flags
- No lot number, or a lot number that does not match the vial.
- A purity figure with no chromatogram, or the same chromatogram reused across different products or lots.
- No mass spectrometry result, or an observed mass that does not match the theoretical value.
- No laboratory name, or a laboratory that cannot be contacted to confirm the report.
- Dates that do not make sense, such as a test date before the lot was made.
- Round, perfect numbers everywhere (for example 100.00% purity) with no supporting data.
Our certificates
Every Omnix Bioscience lot is tested by an independent third-party laboratory, and a certificate of analysis is available for every product. Check that the lot number on your vial matches the certificate. If you cannot find the certificate for your lot, contact us with the lot number and we will send it.