Why Purity Verification Matters
A peptide’s purity percentage is not a marketing figure; it is a measured value that directly affects how the material performs in downstream formulation, clinical dosing, or research use. Impurities can include truncated sequences, deletion products, or diastereomers formed during synthesis, and any of these can affect efficacy, safety, or experimental reproducibility depending on the application.
Buyers who treat the purity figure on a certificate of analysis as simply a number to compare across quotes, without understanding how it was measured, miss important context about what that number actually represents.
HPLC Fundamentals for Peptide Testing
High-performance liquid chromatography separates the peptide from related impurities based on their chemical interaction with a column, producing a chromatogram where the target peptide appears as the dominant peak. The purity percentage reported on a certificate of analysis is typically the area of the main peak relative to the total area of all detected peaks, measured at a specified wavelength.
It is worth asking manufacturers which HPLC method and column they use, since results can vary somewhat between methods, and reputable manufacturers are able to provide the actual chromatogram alongside the summary purity figure rather than only the final number.
Mass Spectrometry for Sequence Confirmation
While HPLC establishes purity, mass spectrometry confirms that the molecule present is actually the intended peptide sequence, by matching the measured molecular weight against the theoretical weight calculated from the sequence. This step catches errors that purity testing alone would miss, such as a structurally similar but incorrect sequence that happens to elute at a similar retention time.
A complete certificate of analysis should include both HPLC purity data and mass spectrometry identity confirmation; a certificate showing only one of the two provides an incomplete picture of the material’s quality.
Reading the Results as a Buyer
When reviewing a certificate of analysis, check that the reported molecular weight matches your expected calculation for the sequence, that the HPLC purity meets your specification, and that the batch number on the certificate matches the physical batch received. Discrepancies in any of these should be raised with the manufacturer before the material is used.
For high-value or regulated applications, some buyers commission independent third-party testing on incoming batches as a routine verification step, rather than relying solely on the manufacturer’s own certificate, particularly for new supplier relationships.