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Everyone says it, but what does “purity” REALLY MEAN?
For peptides, “over 99% purity” sounds simple, but it actually sits at the intersection of chemical purity, identity, salt/counterion form, and endotoxin control. A vial can look “99% pure” by one metric and still be unsuitable for sensitive biology if the wrong impurities, counterions, or endotoxin burden are present. What “>99% purity” usually means Most vendors mean HPLC area-percent purity: the main peptide peak accounts for more than 99% of the integrated chromatogram area. HPLC is the standard method used to assess peptide purity, but it is not a complete description of quality because closely related impurities can co-elute and hide under the main peak. Identity is therefore commonly confirmed separately by mass spectrometry. polypeptide.com genscript.com That matters because 99% HPLC purity is not the same as 99% peptide content by weight. Residual water, trifluoroacetate or acetate counterions, synthesis reagents, and other non-peptidic material may not show up the same way in an HPLC purity number. The peptide industry QC literature explicitly separates purity, identity, and assay/content as different release criteria. polypeptide.com Why salts matter Peptides are often supplied as a salt form, commonly TFA, acetate, or sometimes HCl. That salt is not just packaging trivia – it affects: Net mass in the vial, because part of the measured weight can be counterion rather than peptide. Solubility and handling, since some salt forms dissolve better or behave more gently in certain buffers. Biological compatibility, especially for cell work where residual TFA can be undesirable. Interpretation of dose, because “1 mg peptide acetate” is not exactly the same as “1 mg free peptide base.” So when someone says a peptide is >99% pure, the next question is: 99% pure in what form, and with what peptide content? A solid COA should list the counterion/salt form, peptide content or assay if available, and the analytical methods used. The press release in your search results also highlights COAs documenting purity, identity, endotoxin status, and counterion information, though that source is marketing material rather than a neutral technical reference. einpresswire.com What mass spectrometry does – and does not do Mass spectrometry is mainly for identity confirmation: does the observed molecular mass match the expected peptide? It is valuable because a clean HPLC peak can still belong to the wrong molecule or a truncated/deleted product. At Advanced Peptide Research (APR LABS) We do all the heavy lifting so that you can just worry about the research.
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