Net peptide content
Net peptide content is the share of a lyophilized powder's total weight that is peptide, as opposed to water and counter-ions.
A vial of lyophilized peptide is never 100% peptide by weight. The powder holds residual water, and because peptides are salts, their basic residues carry counter-ions, most often trifluoroacetate left by cleavage and purification, sometimes acetate or chloride. Net peptide content is the fraction of the weighed mass that is the peptide itself, and it is often noticeably lower than the purity figure on the same certificate.
It is a different measurement from purity. HPLC purity counts only what elutes from the column and absorbs at the detection wavelength, so water and counter-ions are invisible to it. A sample can read 99% pure and still carry a substantial share of water and salt by mass, with more counter-ion in sequences that have many basic residues.
The distinction matters most when making solutions to a precise molar concentration. There, net peptide content changes the arithmetic more than the difference between 98% and 99% purity does. Net peptide content is usually determined by amino acid analysis or elemental nitrogen analysis, and most research-grade certificates do not report it, so check whether a certificate's unit mass means total powder or peptide.
Related terms
UPDATED OCTOBER 26, 2026 · REVIEWED BY DEL POTTER, PHD