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    • How-to guides

    How to actually read an HPLC purity report

    The COA thread people keep asking for. Reading an HPLC purity report, step by step:

  • Find the main peak — that's your target compound.
  • Read its area percent. That's the "purity %" everyone quotes.
  • Look at the other peaks (impurities) and their percentages.
  • Check the method block: column, mobile phase, wavelength. A purity number with no method behind it is just a number.

    • Biggest beginner trap: assuming a high purity % alone proves identity. It doesn't — that's what mass spec is for. More on that below.

    Excellent breakdown. To reinforce step 5: purity answers "how much of this is the compound," identity (mass spec) answers "is this the compound at all." You need both. A 99% area-percent peak of the wrong molecule is still the wrong molecule.

    One practical add: glance at the peak shape, not just the number. A clean, symmetric main peak with flat baseline tells a different story than a high number sitting on a noisy, drifting baseline.

    This finally made area percent make sense to me. The "purity high but identity unproven" trap is exactly the thing I'd have fallen into. Bookmarked.

    And check the wavelength in the method. Reading purity off a detection wavelength that doesn't suit the compound can flatter or punish the number. Method block first, always.

    Came here from the area-percent thread — this is the clearest explanation of a COA I've found anywhere. The "purity high but identity unproven" trap finally makes sense. Thank you for writing it.

    This thread does a lot of quiet heavy-lifting for new members — keeping it near the top on purpose. If you're new and reading this: the method block (column, mobile phase, wavelength) is the part people skip and shouldn't.

    Want to join the discussion?

    Related reading

  • How to read a COA
  • >99% purity standards

    • Premium research peptides at >99% HPLC-verified purity, third-party tested by Janoshik Analytical with a Certificate of Analysis on every lot. Shipped lab-direct, discreet and cold-chain, worldwide. For laboratory research use only.

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