How to read a peptide certificate of analysis
Updated
In short
A peptide certificate of analysis documents one specific batch. The two sections that matter most are the HPLC chromatogram, which establishes purity as a percentage of total peak area, and the mass spectrometry result, which confirms the molecule is the sequence it claims to be. A COA without a batch number tying it to the vial in hand is not evidence of anything.
What a COA is, and what it is not
A certificate of analysis reports test results for a single manufactured batch. It is not a product-wide claim and it does not transfer between lots. The useful question when you receive one is always the same: does the batch number on this document match the batch number on the vial?
Section by section
| Section | What it tells you | What to check |
|---|---|---|
| Batch / lot number | Which manufacturing run the document covers | That it matches the vial label exactly |
| HPLC purity | Purity as a percentage of total peak area | The chromatogram itself, not just the headline number |
| Mass spectrometry | That the observed mass matches the expected mass | Observed vs theoretical mass are both stated |
| Appearance | Physical description of the lyophilized cake | Matches what is actually in the vial |
| Water content | Residual moisture after lyophilisation | Relevant to net peptide mass |
| Test date | When the batch was analysed | That it is the batch's own analysis, not a reference run |
Reading the HPLC number honestly
A purity figure such as 99% describes the target peak as a percentage of total peak area in that chromatogram. It says nothing about anything that does not absorb at the detection wavelength, and it says nothing about how much of the vial's total mass is peptide as opposed to residual solvent, counter-ion or water. Peptide content and chromatographic purity are different numbers, and a high value for one does not imply the other.
What a COA cannot tell you
- Whether the compound will behave as expected in your assay. Identity and purity are necessary, not sufficient.
- Whether the vial has been stored correctly since testing. The document describes the batch at the time of analysis.
- Anything about safety in humans or animals. These are research chemicals; a COA is an analytical document, not a safety assessment.
Every batch in this catalogue is tested by an independent US laboratory and verified to exceed 99% purity by HPLC/MS. Contact us with a batch number and we will send that batch's report.
Frequently asked questions
- What does 99% purity on a peptide COA actually mean?
- It means the target peak accounts for 99% of the total peak area in the HPLC chromatogram at the detection wavelength used. It is not a statement about how much of the vial's mass is peptide — residual water, solvent and counter-ion are separate figures.
- Is a COA transferable between batches of the same product?
- No. A certificate of analysis documents one manufacturing batch. A document whose batch number does not match the vial in hand provides no information about that vial.
- What is the difference between HPLC purity and peptide content?
- HPLC purity is the proportion of chromatographic peak area attributable to the target molecule. Peptide content is the proportion of the vial's total mass that is peptide, with the remainder being water, counter-ion and residual solvent. A product can be high in one and lower in the other.
All products referenced are sold for research, laboratory, or analytical purposes only, and are not for human consumption.