They are called “related” because they come from the peptide itself and closely resemble it, which makes them hard to separate. The most common are:
- Deletion sequences: missing one amino acid because a synthesis coupling failed.
- Truncations: chains that stopped before being completed.
- Degradation products: deamidated, oxidised or isomerised forms that appear over time or with heat or moisture.
- Synthesis leftovers: protecting groups that were not removed, dimers or incorrectly formed disulfide bridges.
In the chromatogram they show up as small peaks around the main one. Their sum is what separates, for example, 99% purity from 95%. Mass spectrometry makes it possible to identify them by their mass difference from the correct peptide.
An impurity that closely resembles the peptide may have similar, no or different activity. That is why in research both the total percentage of impurities and the absence of any single abundant impurity matter.
Related terms
Learn it in depth at the Peptide University
- Related impurities and counterions · Module 7
- Classification and solid-phase synthesis · Module 1
Definition for educational and scientific purposes. It is not medical advice or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).