Purity vs. Net Peptide Content: Two Different Numbers
Why a vial labelled with a peptide amount contains more than peptide by weight, and how purity and net peptide content differ.
Two questions
Purity asks: of the peptide-related material detected, what fraction is the target sequence? Net peptide content asks: of the total powder weight, what fraction is peptide at all?
What else is in the powder
Synthetic peptides are typically isolated as salts with counter-ions (for example acetate or trifluoroacetate) and retain some residual water. These contribute to the weight of the powder without being peptide. As a result, net peptide content is usually below 100% even for high-purity material.
Why it matters for research
When accurate concentrations are needed, researchers may account for net peptide content where it is reported, or determine it themselves (for example by amino-acid analysis). A COA that reports only HPLC purity does not provide this figure.
Educational content for laboratory researchers. Products are for research use only and are not for human or veterinary use.