So, even if a peptide is 98% pure, the net amount of peptide may only represent 70-85% of the total weight of the powder depending on its amino acid composition, last purification step and lyophilisation.
For instance, your order 5 mg of NPY from PolyPeptide. If the net peptide content is 80%, you will receive in fact at least 5/0.8= 6.25 mg of powder. The advantage for you is that you have the exact amount of peptide in your vial. Even if you work in a humid area where hydration can change the weight of the powder.
This makes quantitative comparisons of the results obtained in different laboratories possible and facilitates communication between them.
