Unless other requested, all peptides are shipped according to its gross weight. Gross Weight is the actual weight of the lyophilized product. Gross Weight includes any impurities such as residual water and/or salts from the TFA counterions accumulated during the synthesis and purification processes. “Net Weight” is the amount of actual peptide present minus the impurities. In order to find “Net Weight”, an AAA must be performed. What does the purity mean on the HPLC report? The purity of the peptide is determined by HPLC analysis with detection at 220 nm. The purity of the peptide does not take into account water and salts that are usually present in the sample. Other contaminates found with the peptide can range from sequence deletion, truncation or incompletely deprotected sequences. The peptide’s purity is the amount of correct peptide relative to all analytes that absorb at 220 nm.