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What is net peptide content?
The short answer
Net peptide content is the fraction of a powder's mass that is actually peptide, with water, counter-ions and residual salts excluded. Lyophilised peptides typically carry both bound water and a counter-ion such as acetate or trifluoroacetate, so a milligram of powder is never a milligram of peptide. It is measured separately from chromatographic purity.
In detail
The gap is not small. Depending on the peptide and its salt form, a meaningful share of the powder's weight can be counter-ion and moisture — which is why two vials with identical labels and identical purity figures can hold different amounts of peptide.
A supplier who weighs powder rather than peptide will under-deliver in good faith. Quantification against a reference standard measures the peptide, so it catches this without anyone having to allege bad intent.
If a certificate reports only purity and never milligrams, it has not answered the question most buyers actually care about.
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