Net peptide content.

The share of a vial's mass that is actual peptide rather than salts and water.

Net peptide content, sometimes called peptide content or true peptide content, is the proportion of the material in a vial that is actual peptide, as distinct from counterions, residual salts, bound water, and any bulking agents added during manufacturing. It is a different measurement from purity and it answers a different question. Purity asks what fraction of the peptide present is the correct sequence; net peptide content asks how much peptide is present at all. The two can diverge sharply, and a preparation can honestly be described as 99% pure while a substantial share of the vial's mass by weight is not peptide. Synthetic peptides are typically isolated as salts, most often trifluoroacetate or acetate, and they readily absorb atmospheric moisture, so this is normal chemistry rather than adulteration. It is usually determined by amino-acid analysis or nitrogen determination, and pharmaceutical specifications state it explicitly. The reason it belongs in this glossary is that it is the most commonly omitted number on research-supply documentation, and its absence means the stated milligram figure on a label describes gross vial contents rather than peptide. A Certificate of Analysis reporting purity but not peptide content leaves that gap unresolved.