Does 99% purity mean I get 99% of the labeled dose?
No. Purity and how much actual peptide sits in the vial are two different numbers. HPLC purity (the 99% on most COAs) only compares the target peptide against other peptide-related impurities. Per Bachem's QC guide, it says nothing about non-peptide weight. A vial also holds counterions (TFA or acetate salts) and water. Peptide plus counterion plus water is the mass balance, and it adds up to 100%. So a 99% pure peptide can be well under 99% peptide by weight. Bachem says this is normal for peptides rich in basic amino acids (salt formation) and hydrophilic ones that absorb moisture. The number that tracks real content is net peptide content, measured by amino acid analysis, not HPLC purity. For anything about how much to use, ask a licensed provider. These are research-use-only materials.