HPLC purity of research peptides - what does 99% mean
What HPLC purity actually measures, why a bare 99% figure without a method means nothing, and how to compare declarations from different suppliers of research materials.
Purity is the most frequently compared parameter of research materials - and the one most often taken out of context. The percentage on its own says nothing until you know which method produced it and what that method actually measures.
What HPLC measures
High-performance liquid chromatography (HPLC) separates a mixture into its components and displays them as peaks on a chromatogram. Purity is usually calculated as the area of the main peak relative to the total area of all peaks. So '99% (HPLC)' means: the main peak accounts for 99% of the signal detected by the detector under those conditions.
What HPLC does not measure
- Substances that do not absorb at the wavelength used by the detector - they will not appear on the chromatogram at all.
- Water, salt and residual solvent content - these require separate determinations.
- The identity of the material. HPLC says 'homogeneous', not 'this is that molecule' - identity is confirmed by mass spectrometry.
HPLC purity vs. peptide content
These are two different numbers and they are often confused. Chromatographic purity describes proportions within the organic material, whereas peptide content tells you what fraction of the mass in the vial is the peptide itself - the remainder is typically bound water and counterions from the purification process. A material can have 99% purity and a peptide content of around 80% at the same time, and there is no contradiction in that.
How to compare suppliers
- Only compare declarations that state the method - '99%' with no method is not data.
- Check that the certificate covers the batch you are actually receiving, not a 'typical batch'.
- Note whether the supplier publishes the chromatogram at all, or only a number in a table.
Note
We supply these materials for laboratory research use only (RUO) - not for consumption by humans or animals and not for clinical applications. They are not a medicine, a medicinal product or a dietary supplement.
