Glossary
Net peptide content
The actual mass of peptide in a sample, excluding salt, residual water and excipients — measured by amino acid analysis, not HPLC.
Net peptide content is the true mass of peptide present, separate from the counterion salt, residual moisture and any bulking agent that make up the rest of the powder. It is measured by amino acid analysis or nitrogen determination, and is a different number from chromatographic purity: purity tells you what fraction of the material is the target compound, while net peptide content tells you how much target compound there is. A vial can be 99% pure by HPLC and still contain noticeably less peptide by mass than its nominal label, because purity and content answer different questions. A supplier quoting only a purity percentage has given you one of the two numbers.
Covered in depth in Purity versus net peptide content.
Related terms
- Gross peptide weight
- The total mass of powder in a vial, including salt, residual water and any excipient — not the mass of peptide alone.
- Purity (chromatographic)
- The percentage of the main peak's area relative to the total peak area on a chromatogram — a measure of composition, not quantity.
- Amino acid analysis
- A quantitative method that hydrolyses a peptide into its constituent amino acids to measure how much peptide is actually present.
- Acetate salt
- A peptide paired with acetate counterions, the most common and lower-toxicity salt form produced during purification.
- TFA (trifluoroacetate) salt
- A peptide paired with trifluoroacetate counterions, a common salt form left by standard reverse-phase purification.