A certificate of analysis, or COA, is the document that turns a vial of powder into a characterized research material. Without one, a peptide is an unknown quantity; with one, you know what you are working with and can defend your results. Yet COAs are often skimmed rather than read. This guide walks through the key sections of a peptide COA and explains what the figures actually mean.
What a COA Is For
A COA is a per-batch record of the analytical testing performed on a specific lot of material. Its purpose is to document two fundamental questions: is the sample what it claims to be, and how pure is it. Because peptide synthesis is never perfectly clean, every batch can differ slightly, which is why a COA should be tied to the lot in your hand rather than to the product in general.
HPLC Purity
The purity figure on a COA almost always comes from high-performance liquid chromatography, or HPLC. This technique pushes the dissolved sample through a column that separates its components based on how each interacts with the column material. Different molecules emerge at different times, producing a chromatogram of peaks.
Reading the chromatogram
- The main peak represents the target peptide. Its size relative to the total is the basis of the purity percentage.
- Smaller peaks represent impurities, such as truncated sequences or byproducts of synthesis.
- The purity percentage expresses the target peak as a proportion of the whole, so a figure such as 98 percent indicates that the large majority of the material is the intended peptide.
A higher purity figure means fewer unknown variables in your experiment. When comparing materials, the chromatogram itself is worth examining, not just the headline number, because the shape and number of impurity peaks tell a fuller story.
Mass-Spectrometry Identity
Purity tells you the sample is clean, but not that it is the right molecule. That is the job of mass spectrometry. A mass spec measurement determines the molecular weight of the material with high precision.
- The measured mass is compared against the theoretical mass calculated from the intended amino acid sequence.
- A close match confirms that the molecule present is the one expected.
- A discrepancy signals that the material may not be the intended sequence, regardless of how pure it appears.
Identity and purity together form the core of a meaningful COA. One without the other leaves an important question unanswered.
Other Fields Worth Checking
Beyond the two central analyses, a complete COA typically includes several supporting fields:
- Product name and sequence: the identity of the peptide as the supplier intends it.
- Batch or lot number: the link between the document and the specific material.
- Test date: when the analysis was performed, which helps confirm the document corresponds to the current batch.
- Appearance and form: a basic physical description, such as a lyophilized powder.
Checking that the lot number on the document matches the vial is a small step that prevents a common oversight.
Why COAs Matter for Research
The value of any experiment depends on knowing the inputs. If a result cannot be attributed confidently to the intended compound, it cannot be interpreted or reproduced. A COA is what allows a researcher to rule out the material itself as a source of unexplained variation, and it is what allows results from different laboratories to be compared on common ground.
Reading a COA properly takes only a few minutes, and it is one of the most reliable habits a researcher can build. A vial without a current, lot-specific certificate is an unknown, and unknowns have no place in careful work.
For research use only — not for human or veterinary use.