Lyophilized peptides arrive as a dry cake or powder because dry material is far more stable than material in solution. Reconstitution — returning that solid to a liquid of known concentration — is the step where most avoidable losses happen. This guide covers the laboratory practice.
What lyophilization actually does
Freeze-drying removes water by sublimation under vacuum, leaving a porous solid. Because hydrolysis and most degradation pathways need water, the dried peptide is stable for far longer than the same material in buffer. The trade-off is that the cake is hygroscopic: every minute the vial sits open in humid air, it pulls in moisture.
Two practical consequences follow. First, bring the vial to room temperature before you break the seal, or condensation will form on cold glass and start rehydrating the cake on your bench. Second, work efficiently once it is open.
Choosing a diluent
The right vehicle depends on the peptide. The lot-specific Certificate of Analysis is the authority; where it specifies a solvent, use that one.
- Bacteriostatic water — sterile water preserved with benzyl alcohol. The preservative is what makes multi-draw work over days rather than hours. See our comparison of bacteriostatic versus sterile water.
- Sterile water for injection — unpreserved. Appropriate for single-use preparations, or where benzyl alcohol would interfere with an assay.
- Dilute acetic acid — some hydrophobic or poorly water-soluble peptides dissolve far better in a weakly acidic vehicle.
- DMSO — a last resort for peptides that resist aqueous vehicles entirely. Note that DMSO can interfere with downstream assays and is not compatible with every application.
If a peptide will not dissolve in water, do not force it with heat or vigorous agitation. Check the COA, then step to a more appropriate solvent.
Working out the concentration
Concentration is simply mass divided by volume. A vial containing 10 mg of peptide reconstituted in 2 mL of diluent gives 5 mg/mL. Reconstitute the same 10 mg in 5 mL and you have 2 mg/mL.
Two things regularly trip people up:
- Salt form. Most research peptides are supplied as acetate or TFA salts. The gross mass in the vial is therefore higher than the net peptide mass. If your work depends on exact peptide content rather than gross vial mass, read the net peptide content figure on the COA.
- Displacement. The solid itself occupies volume. For small quantities in a few millilitres this is negligible, but for concentrated preparations it is not.
Technique
- Bring the vial to room temperature, sealed.
- Sanitise the stopper and let it dry.
- Add the diluent slowly, directing the stream against the inside wall of the vial rather than straight onto the cake. A jet of liquid hitting the solid directly causes foaming, and foaming means denatured peptide at the air-liquid interface.
- Let it stand. Many peptides dissolve unaided within a few minutes.
- If material remains, swirl gently or roll the vial between your palms. Do not shake, and do not vortex a peptide solution unless a protocol specifically calls for it.
- Inspect against a light source. A properly reconstituted solution should be clear and free of visible particulates.
Common mistakes
- Shaking. Mechanical shear and the air-liquid interface both denature peptides. Swirl instead.
- Heating. Warming may appear to speed dissolution while quietly degrading the material.
- Skipping the label. Record the compound, lot number, concentration and reconstitution date on the vial. An unlabelled vial in a shared fridge is worthless.
- Repeated freeze-thaw. Each cycle costs you material. If a preparation will be drawn on repeatedly, aliquot it once and freeze the aliquots.
- Ignoring the COA. Solubility genuinely varies between compounds, and in a few cases between lots.
After reconstitution
Reconstituted material is generally stored at 2-8 °C and protected from light, with longer-term storage at -20 °C in single-use aliquots. Specific windows are on each product page and on the COA. Our guide to storing research peptides covers this in detail.
This article covers laboratory handling practice only. All materials supplied by Never Enough Labs are for in-vitro research use by qualified persons 21 years of age or older. Nothing here is medical, veterinary or diagnostic guidance, and no product described is intended for human or animal use.