Peptide reconstitution calculator

What reconstitution means

Peptides are supplied lyophilised: freeze-dried to a solid so the material stays stable in transit and in storage. Before any analytical or laboratory work the solid has to be dissolved, and that step is called reconstitution. The volume of diluent added is what sets the concentration of the resulting solution: the same 10 mg vial becomes a 10 mg/mL solution in 1 mL of diluent, or a 2 mg/mL solution in 5 mL.

Nothing about the vial changes when you add more or less diluent — the mass of peptide is fixed. What changes is how much liquid carries a given mass, and therefore how precisely small amounts can be measured out.

How the arithmetic works

Three relationships are all that is involved, and the calculator above simply applies them:

• Concentration = peptide mass ÷ diluent volume. A 10 mg vial in 2 mL gives 5 mg/mL, which is 5000 µg/mL.
• Volume per aliquot = target aliquot ÷ concentration. A 250 µg aliquot drawn from a 5000 µg/mL solution occupies 0.05 mL.
• Syringe units = volume in mL × 100, because a 100-unit graduated syringe divides 1 mL into 100 marks. That 0.05 mL reads as 5 units.

The practical consequence is worth noting: a more dilute solution spreads the same mass over more liquid, so each aliquot occupies more graduations and small measurement errors matter less in relative terms. Working too concentrated pushes aliquots down to one or two graduations, where the syringe's own tolerance becomes the dominant source of error.

Choosing a diluent

Published protocols most often use bacteriostatic water — water containing 0.9% benzyl alcohol, which suppresses microbial growth and therefore suits a solution that will be stored and accessed more than once. Sterile water without a preservative is used where a solution is prepared and consumed in a single session. Some peptides that dissolve poorly in water are described in the literature as being brought into solution with a small volume of acetic acid or another solvent first; the certificate of analysis or the source publication for the compound is the reference for those cases.

Direct the stream of diluent against the wall of the vial rather than onto the lyophilised cake, and let the solid dissolve without shaking. Peptides are sensitive to mechanical stress and vigorous agitation is reported to promote aggregation and loss of intact material.

After reconstitution

A solution is markedly less stable than the dry solid. Reconstituted peptide is generally held refrigerated at 2–8 °C for short-term work and frozen at −20 °C or below for longer periods, protected from light. Repeated freeze–thaw cycling is the failure mode most often described in stability work, which is why aliquoting into single-use volumes at the time of reconstitution is standard practice. Our reconstitution and storage guide covers diluents, temperatures and traceability in more depth.

Record the batch number, the diluent used, the volume added and the date on the vial itself. Without that, a solution found in a freezer weeks later is not traceable to a certificate of analysis, and any measurement made from it is unattributable.

Before you calculate anything

The calculator assumes the vial contains the mass printed on the label. That assumption is only as good as the documentation behind it, which is why the mass and the purity on the certificate of analysis for your specific batch are the figures to work from — not the marketing description. If you are evaluating a supplier, our guide on sourcing research-grade Semax in Europe sets out what a valid certificate has to state.

All material listed in our catalogue is supplied for laboratory research use only and ships with a batch-specific certificate of analysis.