Peptide Purity
The percentage of a sample consisting of the intended target peptide. Pharmaceutical-grade peptides require above 98-99% purity. Research-grade peptides range from 95% to over 99%. Impurities may include truncated sequences, deletion sequences, oxidised forms, or racemised amino acids.
Technical Context
Purity specifications depend on application: pharmaceutical grade (>98-99%, with individual specified impurities <0.5% and total impurities <2%), clinical trial material (>95-98%), research grade (>95%), and custom synthesis (variable, 70-98%). Impurity types: deletion peptides (missing one amino acid — caused by incomplete coupling), truncated sequences (synthesis terminated prematurely), insertion peptides (double coupling of an amino acid), oxidation products (Met→Met(O), Trp→oxyindole), deamidation products (Asn→Asp/isoAsp, Gln→Glu), racemisation (L→D at activated positions), and TFA/acetonitrile residues from purification. ICH Q3A/B impurity guidelines define: reporting threshold (above which impurities must be identified), identification threshold (requiring structural characterisation), and qualification threshold (requiring toxicological evaluation). For biotechnology products, ICH Q6B provides specific quality attribute guidance.