It is important to understand the difference between net peptide content and total peptide content. The dry peptide powder shipped to you usually contains not only peptide, but also some other substances such as water, absorbed solvents, counter ions and salts. The total peptide content(gross weight) refers to the weight of this mixture. Net peptide weight indicates the actual weight of the peptide component of your sample. Net peptide content is usually 50-80% of the total peptide weight (also called gross peptide weight) and is usually determined by amino acid analysis or UV spectrophotometry. Net peptide content should not be confused with purity. Purity defines the percentage of the target peptide sequence in the peptide component of your sample.