How much peptide is really in the vial?
A 10 mg vial at 99% purity does not hold 9.9 mg of peptide. Part of the powder is counterion salt left over from purification, and part is bound water. Enter a sequence to estimate the real peptide mass.
10.0 mg × 81.9% × 98.5% = 8.06 mg · content = 1419.55 ÷ (1419.55 + 2 × 114.02) × (1 − 5%)
Purity and net content measure different things
HPLC purity is the share of the target peptide among peptide-related peaks. Truncated and deletion sequences lower it. Salts and water are invisible to it.
Net peptide content is the share of total powder weight that is peptide. The rest is counterions, water and sometimes a bulking agent such as mannitol. To get the target peptide mass you need both: powder mass × net content × purity.
Theoretical peptide share by salt form
Dry salt only, assuming one counterion per basic site.
| Peptide | MW | Basic sites | TFA | Acetate | HCl |
|---|---|---|---|---|---|
| BPC-157 | 1419.55 | 2 | 86.2% | 92.2% | 95.1% |
| GHK (tripeptide) | 340.38 | 3 | 49.9% | 65.4% | 75.7% |
| Angiotensin II | 1046.19 | 3 | 75.4% | 85.3% | 90.5% |
| Bradykinin | 1060.22 | 3 | 75.6% | 85.5% | 90.6% |
Questions to ask a supplier
- Is the price per mg of powder (gross) or per mg of peptide (net)?
- Which salt form is it: TFA, acetate or HCl?
- Is net content measured, and by which method (amino acid analysis, nitrogen, quantitative HPLC)?
- Does the labelled amount include an excipient?
Limits of the estimate
The calculator assumes one counterion per basic site and uses average residue masses for unmodified, linear peptides with a free C-terminal acid. Amidated, cyclic, lipidated or PEGylated peptides need the supplier's own data. A measured content value on the COA beats this estimate. This is arithmetic on the numbers you enter, not dosing or safety guidance.