A synthetic peptide never comes out of synthesis at 100%: alongside the correct molecule there are chains one amino acid short, truncated chains, oxidised forms or forms with a leftover protecting group. Purification removes most of them, and purity measures what remains: the percentage of the chromatogram area that belongs to the main peak.
Typical ranges in the research market go from 95% to 99% or more. The difference looks small, but going from 95% to 99% means cutting impurities from 5% to 1%: five times less foreign material.
Purity must not be confused with quantity. A 10 mg vial at 99% purity does not contain 9.9 mg of peptide: the freeze-dried powder also includes water and counter-ions, and that is measured by a different parameter, peptide content.
A purity figure is only worth something if it is backed by a chromatogram of the specific batch. “Guaranteed purity” without a certificate, or a generic certificate with no batch number, provides no verifiable information.
Related terms
Learn it in depth at the Peptide University
- HPLC: the measure of purity · Module 7
- Peptide content, water, counterion and reading the COA · Module 7
- Mass spectrometry and identity · Module 7
- Related impurities and counterions · Module 7
- Pharmacovigilance, quality and evidence-based practice · Module 10
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).