Research Use Only. All materials supplied by AbsoluteBioLab are for in vitro laboratory research only. This guide explains the arithmetic behind concentration and dilution calculations for reconstituted research peptides. It does not provide dosing, injection volume or treatment guidance.
Research Peptide Concentration and Dilution Calculations
Preparing a peptide solution at a defined concentration requires knowledge of the molecular weight, the mass of material, the target concentration and the target volume. This guide explains the underlying arithmetic and the variables that affect accuracy, without prescribing product-specific recipes or administration volumes.
Core equations
Mass to molar concentration
To calculate the molar concentration of a solution prepared from a known mass:
Concentration (µM) = [mass (µg) / molecular weight (g/mol)] / volume (mL) × 1000
Required volume for a target concentration
To calculate the volume of solvent needed to achieve a target concentration from a known mass:
Volume (mL) = mass (µg) / [target concentration (µM) × molecular weight (g/mol)] × 1000
Dilution (C1V1 = C2V2)
To prepare a working solution from a concentrated stock:
Volume of stock needed = (target concentration × target volume) / stock concentration
Variables that affect calculation accuracy
| Variable | Impact on calculation | How to account for it |
|---|---|---|
| Molecular weight (free base vs salt form) | Using the wrong MW gives an incorrect molar concentration. | Use the MW for the actual form supplied (including counter-ion if applicable). Check the CoA or product specification. |
| Net peptide content vs total mass | The weighed mass includes counter-ions, water and non-peptide material. | If net peptide content is stated on the CoA, use it to correct the effective peptide mass. See Counter-Ions and Peptide Content. |
| Weighing accuracy | Small masses (<1 mg) are difficult to weigh accurately on standard balances. | Use an analytical balance with appropriate precision. Consider dissolving the entire vial contents and calculating from the labelled mass. |
| Volume measurement | Pipetting accuracy affects the final concentration. | Use calibrated pipettes appropriate for the volume range. |
| Solubility | If the peptide does not fully dissolve, the effective concentration is lower than calculated. | Verify complete dissolution visually and, where possible, analytically. See Solvent and Buffer Compatibility. |
Worked example (in vitro laboratory context)
A researcher needs to prepare a 100 µM stock solution from 5 mg of a peptide with MW = 1200 g/mol (free base form).
- Convert mass to micrograms: 5 mg = 5000 µg
- Calculate moles: 5000 µg / 1200 g/mol = 4.167 µmol
- Calculate volume for 100 µM: 4.167 µmol / 100 µM = 0.04167 L = 41.67 mL
This example assumes 100% peptide content. If the net peptide content is 80%, the effective peptide mass is 4000 µg and the required volume adjusts to 33.33 mL for the same target concentration.
Interactive calculator
The AbsoluteBioLab Peptide Calculator provides an interactive tool for performing these calculations. Enter the molecular weight, mass and target concentration to obtain the required volume. The calculator performs the arithmetic described above.
What this guide does not provide
- Product-specific reconstitution recipes (these require verified product data)
- Injection volumes, syringe-unit conversions or dose-per-bodyweight calculations
- Universal solvent recommendations (see Solvent and Buffer Compatibility)
- Guidance for human or veterinary administration
Frequently asked questions
Should I use the free-base MW or the salt-form MW?
Use the molecular weight that corresponds to the actual form of the material supplied. If the product is supplied as a TFA salt, the effective MW includes the TFA contribution. Check the product specification or CoA for the stated form.
What if I cannot weigh the peptide accurately?
For small quantities, consider dissolving the entire vial contents and using the labelled mass for calculation. This avoids weighing error but assumes the labelled mass is accurate.
Does the calculator account for net peptide content?
The interactive calculator performs the basic mass/MW/volume arithmetic. If net peptide content differs from 100%, apply the correction factor manually to the mass input.
