What’s difference between polypeptide content and polypeptide purity?

A polypeptide product includes polypeptide itself, water and impurities such as organic salt introduced in the production process. The purity of the polypeptide refers only to the content of the peptide and the impurities, excluding water; while the content of polypeptide refers to the net content of the target polypeptide in the product, which is generally detected by N-element analysis or amino acid molecule; therefore, even if the purity of a polypeptide reaches 99%, its content may be only 70-80% because of the existence of water, organic salt, etc.