A reconstitution calculator for laboratory preparation of lyophilised research reference materials. Enter the mass in the vial and the volume of diluent added, and the calculator returns the resulting concentration and the volume that contains a given mass. All figures are laboratory preparation values only.
Calculated on the assumption that the lyophilised solid contributes negligible volume, which is the standard working assumption at these masses. Verify against the batch Certificate of Analysis for the actual peptide content of your vial, which may differ from the nominal label mass because of counter-ion and residual solvent content.
How the calculation works
Reconstitution is a dilution problem. The mass of solid in the vial is fixed; the concentration of the resulting solution is determined entirely by the volume of diluent added:
Concentration = mass in vial ÷ volume of diluent
A 10 mg vial reconstituted in 2 mL of diluent gives 5 mg/mL, or 5000 µg/mL. To withdraw 250 µg from that solution you take 0.05 mL (50 µL). Changing the diluent volume changes the concentration and therefore the volume you withdraw — it does not change the total mass available in the vial.
Choosing a diluent volume
Two competing considerations set the working volume. Smaller volumes give higher concentrations, which means smaller withdrawal volumes and greater relative pipetting error. Larger volumes give lower concentrations, larger and more accurately measurable withdrawal volumes, but a shorter usable window once the vial is in solution and more freeze-thaw exposure if the material is aliquoted and stored.
In practice most laboratory protocols select a volume that puts routine withdrawals in the 20–200 µL range, where standard air-displacement pipettes are accurate. If your protocol calls for repeated withdrawals over an extended period, aliquoting into single-use volumes immediately after reconstitution avoids repeated freeze-thaw cycles on the whole stock.
Nominal mass and actual peptide content
The mass printed on a vial is the nominal fill mass of the lyophilised solid. That solid is not pure peptide by mass: it also contains counter-ions from the final purification step (commonly trifluoroacetate or acetate) and residual water. Peptide content by mass is therefore typically lower than the label figure, and the exact figure varies by sequence and by batch.
Where a calculation must be based on actual peptide mass rather than nominal fill mass, the batch Certificate of Analysis is the reference document. It reports the analytical results for the specific batch in front of you, not a generic specification. Batch-to-batch variation in peptide content is a well-documented source of irreproducibility in published work; see batch variability in peptide synthesis for the underlying causes.
Diluent selection and storage
Bacteriostatic water — water containing 0.9% benzyl alcohol — is the common choice where a reconstituted stock will be sampled more than once, because the benzyl alcohol suppresses microbial growth in the vial between withdrawals. Sterile water without a preservative is used where a single withdrawal is made and the remainder discarded, or where benzyl alcohol would interfere with the assay. Some sequences require a specific buffer or a small percentage of acetic acid to dissolve fully; the product page and the Certificate of Analysis are the reference for sequence-specific requirements.
Once in solution, peptides degrade faster than they do as a lyophilised solid. Storage conditions, light exposure and the number of freeze-thaw cycles all matter, and they matter more for some sequences than others. Storage and handling of research peptides covers the conditions in detail.
Worked examples
| Vial | Diluent | Concentration | Volume for 250 µg | Volume for 500 µg |
|---|---|---|---|---|
| 5 mg | 1 mL | 5 mg/mL | 50 µL | 100 µL |
| 5 mg | 2 mL | 2.5 mg/mL | 100 µL | 200 µL |
| 10 mg | 2 mL | 5 mg/mL | 50 µL | 100 µL |
| 10 mg | 5 mL | 2 mg/mL | 125 µL | 250 µL |
| 30 mg | 3 mL | 10 mg/mL | 25 µL | 50 µL |
Frequently asked questions
Does the calculator account for the volume of the solid?
No, and neither do standard laboratory protocols at these masses. A 10 mg lyophilised plug displaces on the order of 10 µL, which is below the measurement error of the reconstitution step itself. Where displacement matters — at much higher masses or in very small volumes — the volume should be measured after reconstitution rather than calculated.
Why does my calculated concentration differ from the label?
The most common reason is that the label figure is nominal fill mass rather than assayed peptide content. The second most common is inaccurate diluent measurement: adding 2.2 mL where 2.0 mL was intended changes the concentration by 10%.
Can I re-lyophilise and re-reconstitute?
Re-lyophilisation is possible but is not a neutral operation — it introduces an additional handling step and, for some sequences, measurable degradation. Where a stock will be used across multiple sessions, aliquoting at the point of first reconstitution is the more common approach.
Research use only. The materials referred to on this page are supplied for in vitro laboratory and scientific research use only. They are not medicines, are not for human or veterinary use, and are not for use in any form of diagnosis or treatment. Nothing on this page is a dosing instruction or a protocol for administration to any living organism.
