Work out the concentration produced by reconstituting a lyophilised vial in a given volume of solvent, and what each withdrawal then represents.

What the calculation is

Concentration is vial contents divided by solvent volume. The quantity in a withdrawal is that concentration multiplied by the volume withdrawn. Neither figure accounts for residual volume left in the container, so treat the withdrawal count as an upper bound.

Two things the arithmetic does not know

Solubility. A concentration that is arithmetically valid may not be achievable. Some peptides will not go into solution at neutral pH at higher concentrations, which is why two reconstitution solvents are stocked rather than one — see the format guide.

Stated mass versus peptide content. A vial labelled at a given mass contains that mass of supplied material. Residual moisture and counter-ions mean peptide content can be lower, which is why water content appears on the certificate.