Understanding Peptide Purity Standards

Purity specification is the single most misunderstood parameter in peptide ordering. Here's what those percentages actually mean in practice.

How Purity Is Measured

Peptide purity is determined by analytical HPLC, typically using a C18 reversed-phase column with UV detection at 220 nm. The main peak area divided by total peak area gives you the purity percentage.

Common Grades And When To Use Them

>85% — Suitable for initial screening, epitope mapping libraries, and assays where minor impurities won't affect results.

>95% — The standard for most research applications. Cell-based assays, binding studies, and in vivo work at early stages.

>98% — Required for structural studies, NMR, sensitive enzymatic assays, and any work where impurities could confound results.

Impurities That Don't Show On HPLC

Deletion sequences, racemized residues, and wrong-sequence contaminants may co-elute with the main peak. This is why MS confirmation is essential alongside HPLC — not optional.

Our Recommendation

Match purity to your application, not your budget. Ordering >98% when >95% suffices wastes money. Ordering >95% when you need >98% wastes months of research.