What HPLC purity and mass-spec identity tell you
Two tests, two different questions: how much of the sample is the target, and is it the right molecule.
Most peptide certificates of analysis rest on two measurements: HPLC purity and mass spectrometry identity. They are often reported side by side, but they answer different questions. Understanding the difference helps you judge what a certificate does and does not show.
HPLC: separating the sample
High-pressure liquid chromatography pushes a dissolved sample through a packed column. Different molecules interact with the column material to different degrees, so they leave the column at different times. A detector, commonly measuring ultraviolet absorbance, records a signal as each component exits. The finding is a chromatogram: a line with peaks, each peak representing a component of the sample.
What the purity number means
The purity value is usually the area of the main peak divided by the total area of all peaks, expressed as a percentage. It tells you how dominant the target compound is among the components the detector can see. It does not, on its own, prove which molecule the main peak is. Two different substances could in principle produce similar retention times. That is why purity is paired with an identity test.
Mass spectrometry: weighing molecules
Mass spectrometry converts molecules in the sample into charged particles and measures their mass-to-charge ratio. For a peptide, the expected molecular weight can be calculated from its sequence and any modifications. If the observed mass matches the expected mass within the instrument’s tolerance, that is strong evidence the sample contains the intended molecule. Larger peptides often appear as several charged forms, which the software combines into one mass.
Why you need both
Identity without purity tells you the right molecule is present but not how much of the sample it represents. Purity without identity tells you one component dominates but not what it is. Together, they give a reasonable picture: the dominant component is the intended peptide, and it accounts for a stated share of the detected material.
Limits to keep in mind
Neither test measures everything. HPLC purity reflects what the detector responds to under the chosen conditions. Water and salts that are present in a weighed powder are generally not counted in the HPLC percentage, which is why net peptide content can differ from the gross weight. Findings also describe one lot on one date, which is why lot numbers matter so much.
Putting it into practice
When you review a certificate, look for the named method, the purity value, the expected and observed masses, and the lot number. If you want help reading a specific certificate, contact our team and quote the lot number. See also How to read a certificate of analysis.
Educational content for laboratory research. Bio Elevate products are for research use only and are not for human or veterinary use.