Laboratory literacy · 2 min
Peptide COAs: why purity is not the same as identity
What HPLC and mass spectrometry can tell you about a peptide sample—and why a high purity percentage does not prove identity, sterility, or suitability.
The short version
A purity result and an identity result answer different questions. Read each alongside its analytical method and the exact sample tested; neither is a blanket assurance that a product is suitable for human use.
Research use only. Educational reference to published literature—not medical advice or a guide to human use.
What a purity percentage actually describes
Chromatography separates components of a sample. An HPLC purity result often expresses the area of a selected peak relative to the detected peaks under that method. It is a measurement with a reporting basis—not an all-purpose statement about everything in the vial.
Ask which detector, method, and calculation were used. A peak-area percentage should not automatically be read as the percentage of the vial's total mass that consists of the intended peptide. Different analytical questions require different measurements.
Identity is a separate analytical question
Mass spectrometry provides evidence about molecular mass and, depending on the technique, structural features. A mass consistent with the expected molecule is useful evidence, but a mass match alone does not necessarily resolve every sequence or structural ambiguity.
This is why a report showing a high chromatographic percentage without an identity result leaves an important question unanswered. Purity concerns the composition measured by an assay; identity concerns whether the material matches the intended molecule.
Sources: [1]
The result belongs to the sample tested
A study of synthetic quorum-sensing peptides compared supplier documentation with independent analyses and found discrepancies in the materials examined. Its value is as a concrete example of why documentation and characterization deserve scrutiny—not as an estimate of the quality of all peptide products.
Match the certificate's sample identifier and batch information to the material under discussion. A report for a different lot, an unspecified sample, or a reference standard does not establish the composition of another vial.
Sources: [2]
What the certificate does not establish
HPLC and mass characterization do not substitute for separate evidence about sterility, endotoxins, or biological safety. A COA supports only the attributes actually measured with suitable methods. An unreported attribute is unknown, not automatically satisfactory.
There is no universal purity threshold in this article. Interpretation depends on the intended research question, method suitability, and documentation. Use the companion COA guide to examine a report's fields, rather than treating a single large percentage as the conclusion.
Sources & further reading
- 01Characterization of Synthetic Peptides by Mass Spectrometry (opens in a new tab)
- 02Quality evaluation of synthetic quorum sensing peptides used in R&D (opens in a new tab)
- 03Impurity profiling quality control testing of synthetic peptides using liquid chromatography-photodiode array-fluorescence and liquid chromatography-electrospray ionization-mass spectrometry: the obestatin case (opens in a new tab)