When you buy a peptide with 95% purity, the remaining 5% consists of impurities. These are not inert filler. They are typically truncated sequences, deletion peptides, oxidized forms, or diastereomers of the target molecule.
These impurities can introduce confounding variables into research. A truncated peptide sequence may have partial biological activity, no activity, or even antagonistic activity compared to the target peptide.
HPLC purity is the standard measurement. A peptide listed at 99.5% purity means that 99.5% of the material detected by the HPLC instrument is the correct target sequence. The higher the purity, the more confident you can be in attributing observed effects to the intended compound.
For most research applications, 98% or higher purity is recommended. For sensitive assays, cell culture work, or dose-response studies, 99%+ purity minimizes the risk of impurity-driven artifacts in your data.
Always request and review the Certificate of Analysis before using a peptide in critical experiments. Look at both the HPLC purity percentage and the mass spectrometry data confirming molecular identity.
Disclaimer: This article is for educational purposes only. All peptides are sold for laboratory research use only. Not for human consumption.