Purity is the single most important quality metric for a research peptide, yet it is frequently misunderstood. This reference explains what purity means and how it is measured.
What purity percentage means
Purity is the percentage of the target peptide relative to related impurities (truncated sequences, deletion products, residual solvents, and salts) measured by HPLC. A vial labeled “98%” should contain at least 98% target peptide by peak area.
High-performance liquid chromatography (HPLC)
HPLC separates molecules by retention time and is the standard purity assay. Reputable suppliers report an HPLC chromatogram for every lot. Review both the stated percentage and the trace itself—a clean dominant peak with small impurity peaks is reassuring.
Mass spectrometry (MS)
Mass spectrometry confirms molecular identity by measuring molecular weight. HPLC tells you how much target is present; MS confirms the molecule is what the label claims. Both are needed—high HPLC purity with the wrong mass indicates a mislabeled product.
Nuclear magnetic resonance (NMR)
NMR provides detailed structural confirmation and is more common for complex or novel sequences and GMP-grade API. It is not always supplied for routine catalog research peptides, but can be requested for high-value orders.
Typical grades
- ≥95% (research grade): suitable for most in vitro and animal research
- ≥98% (high purity): preferred for sensitive assays and publications
- GMP grade: manufactured under validated quality systems for regulated work
Always match the documentation to the lot number on your vial, and remember that peptide content (net peptide vs. acetate/HCl salt) is a separate figure from chemical purity.