Lyophilization (freeze-drying) removes water from a peptide to produce a stable powder for storage and transport. Before a lyophilized reference material can be measured in solution, it must be reconstituted — dissolved in a measured volume of solvent to produce a solution of known concentration. This document describes the general laboratory procedure and the arithmetic involved. It is intended for research documentation only.
Choosing a solvent
Bacteriostatic water (sterile water containing 0.9% benzyl alcohol) and sterile water are the most commonly referenced reconstitution solvents for laboratory work. Some peptides with limited aqueous solubility are instead documented with dilute acetic acid or other laboratory-grade solvents. The appropriate choice depends on the physical chemistry of the specific peptide and the requirements of the protocol in use.
The concentration equation
Concentration is total peptide mass divided by solvent volume. If a vial contains 10 mg of peptide and 2 mL of solvent is added, the resulting concentration is 5 mg/mL, or 5,000 mcg/mL. Adding less solvent produces a more concentrated solution; adding more produces a more dilute one. The mass of peptide in the vial does not change — only the volume it is dissolved in.
- Concentration (mg/mL) = peptide mass (mg) ÷ solvent volume (mL)
- Concentration (mcg/mL) = concentration (mg/mL) × 1,000
- Volume to draw (mL) = target amount (mcg) ÷ concentration (mcg/mL)
Handling notes
Add solvent slowly, directing it against the wall of the vial rather than directly onto the peptide pellet, and allow the material to dissolve without vigorous shaking. Gentle swirling is generally preferred. Reconstituted solutions are typically documented as being stored refrigerated and protected from light, with handling kept to controlled laboratory conditions.
The choice between bacteriostatic and sterile water depends on the protocol and the peptide's solubility rather than on the arithmetic above.
Documentation
Record the lot number, the mass stated on the Certificate of Analysis, the solvent and volume used, the date of reconstitution, and the calculated concentration. Consistent record-keeping allows results to be reproduced and cross-referenced against third-party testing data.
Frequently asked questions
What does reconstituting a lyophilized peptide mean?
Reconstitution is the laboratory step of dissolving a freeze-dried peptide powder in a measured volume of solvent to produce a solution of known concentration. The dry powder itself is stable for storage, so it is dissolved only when a measured liquid preparation is required for documentation or analysis.
How do you calculate peptide concentration after reconstitution?
Divide the peptide mass stated on the Certificate of Analysis by the solvent volume added. A 10 mg vial reconstituted with 2 mL of solvent yields 5 mg/mL, or 5,000 mcg/mL. Multiplying milligrams per millilitre by one thousand converts the figure to micrograms per millilitre for finer measurements.
Which solvent is referenced for reconstituting peptides?
Bacteriostatic water and sterile water are the two most commonly documented solvents. Some peptides with limited aqueous solubility are instead referenced with dilute acetic acid. The appropriate choice depends on the physical chemistry of the specific peptide and the requirements of the laboratory protocol being followed.
How should a reconstituted peptide solution be stored?
Documentation commonly references refrigerated storage, often cited around 2–8 °C, with protection from light and a limited usable window. Because reintroducing water can increase the potential for degradation, solutions are usually prepared in quantities that match the timeframe of the protocol rather than in large batches.
What details should be recorded during reconstitution?
Record the lot number, the mass stated on the Certificate of Analysis, the solvent type and volume used, the date of reconstitution, and the calculated concentration. Consistent record-keeping lets results be reproduced and cross-referenced against third-party testing data for the specific lot in hand.