01 · Preparation
Before you begin
- Confirm the compound, batch and chemical form against the vial and its documentation.
- Let a sealed cold vial equilibrate to room temperature in dry conditions before opening. Limit exposure to moisture and reseal promptly.
- Identify the measured peptide amount for your calculation. HPLC purity and net peptide content describe different properties; neither should be substituted for a measured mass without checking the report.
- Prepare the solvent, suitable labware and a record of the intended stock concentration before starting.
02 · Solvent selection
Select a compatible solvent
Use the compound-specific solubility instructions first. Sequence charge and hydrophobicity help guide an initial screen, but modifications and the intended assay also matter.
Basic sequences
Water may be suitable; an acidic aqueous medium can help when the peptide remains insoluble.
Acidic sequences
A basic aqueous medium may improve dissolution. Check residue-specific restrictions before changing pH.
Neutral or hydrophobic sequences
A compatible organic co-solvent may be needed before aqueous dilution. Account for the co-solvent in the final assay.
These are screening principles, not a universal formulation. Cysteine-containing peptides, for example, need particular care when selecting alkaline media and organic solvents.
03 · Technique
Prepare the solution
- Follow the material's documented solvent and handling method. Add solvent gradually, directing it along the container wall.
- Mix gently and allow time for dissolution. Avoid unnecessary foaming; use additional mixing methods only when appropriate for the compound.
- Inspect the preparation for persistent particles or cloudiness before using it as a defined stock.
- Record the final solution volume, solvent composition and any pH adjustment. Include every solvent addition in the concentration calculation.
04 · Stock arithmetic
Calculate the concentration
Divide peptide mass in milligrams by final solution volume in milliliters. If measured mass is available, use the figure for the matching batch.
Example: 10 mg in a final volume of 2 mL
10 mg ÷ 2 mL = 5 mg/mL
A 0.05 mL laboratory aliquot contains 0.25 mg, or 250 µg.
If the measured amount were 10.6 mg, the same final volume would give 5.3 mg/mL. In the stock calculator, that is 106% of a 10 mg label.
05 · Troubleshooting
Resolve solubility problems
- Persistent cloudiness: review solvent compatibility, pH and concentration. Appearance alone cannot establish identity or purity.
- Precipitation after dilution: check how the final buffer and co-solvent fraction differ from the starting stock.
- Material remains undissolved: consult the compound's solubility report before further treatment; do not assume the nominal mass is all in solution.
Supplier solubility data should guide changes to the preparation.
06 · After preparation
Label, aliquot and store
Record the compound, batch, concentration, solvent, preparation date and storage conditions. Divide the stock into portions appropriate for the planned experiments.
Stability depends on the sequence and formulation. Solutions generally have a shorter useful storage life than lyophilized material. Avoid repeated freezing and thawing, protect sensitive material from light and air, and follow the compound's documented temperature and stability limits.
Reconstitution questions
Can every peptide use the same solvent?
No. Use its solubility information and account for the sequence, chemical form and assay conditions.
Should I calculate from the label or the measured mass?
Use a batch-matched measured peptide amount when available. Record when a calculation relies on the label value.
Is HPLC purity the same as peptide content?
No. Counter-ions and residual moisture contribute to powder mass, so analytical purity and net peptide content are different quantities.
What if the solution remains cloudy?
Review the material's solubility report and the preparation conditions before treating it as a known-concentration stock.
How long can I store a prepared stock?
Use the stability information for that compound and solvent. A general storage range is not a verified expiry date for every peptide.
Where can I check the solution arithmetic?
The stock calculator converts peptide mass and volume to concentration. The dilution calculator and aliquot planner continue the workflow.
For in vitro laboratory research. Not for human or veterinary use.
