Ordering a custom peptide means choosing a purity grade — and it is tempting to assume higher is always better. It is not. Higher purity costs more and yields less, so the right grade is the one your application actually needs. Here is how to read the numbers and decide.
What “purity” actually measures
Peptide purity is normally reported as the percentage of the target peptide by HPLC peak area — effectively, what fraction of the peptide material is your sequence versus related impurities. It is measured by analytical HPLC, with identity confirmed by mass spectrometry. Note that purity (relative) is different from net peptide content (absolute), which accounts for water, salts and counterions.
Which grade for which application
- ≥ 80%: early feasibility, antibody screening, non-quantitative work.
- 90–95%: antibody production, ELISA/RIA, many in vitro and in vivo studies.
- ≥ 95%: quantitative assays, receptor-ligand and enzyme studies, reference peptides.
- ≥ 98–99%: structural studies, sensitive quantitative work, and material heading toward clinical use.
Key point: match purity to the application. Paying for 99% when 95% would do is one of the most common ways to overspend on peptides.
The cost and yield implications
Each step up in purity demands tighter preparative HPLC collection, which discards more material and lowers yield — a primary cost driver. The jump from 95% to 99% can be disproportionately expensive for sensitive sequences.
Choosing with your manufacturer
The best approach is to tell your supplier what the peptide is for and let them recommend a grade — and to remember that grade is separate from research vs GMP, which is about the quality system, not the purity number. A good CDMO will right-size both.