Choosing a reconstitution solvent: bacteriostatic water, sterile water, saline, or something else?

Most lyophilized peptides arrive inert. Nothing useful happens until you add a solvent, and the solvent choice has real downstream consequences — for solubility, shelf life after reconstitution, and for the experiment itself. Here is how we think about it.

Bacteriostatic water

Bacteriostatic water is sterile water plus 0.9% benzyl alcohol as a preservative. It is the default for multi-use vials because the benzyl alcohol inhibits microbial growth during the 2–8 °C refrigerated storage that follows reconstitution. For most peptides a solution can stay stable for several weeks under those conditions.

There are caveats. Benzyl alcohol interferes with some downstream assays — if your protocol is sensitive to small aromatic molecules, check first. It also has a faint odour some researchers dislike.

Sterile water and 0.9% sodium chloride

Sterile water for injection or 0.9% saline are both acceptable for same-day reconstitution. They are a good choice if the solution will be consumed within 24 hours, or if the experiment requires a solvent with no preservative. The downside is shelf life: without the bacteriostatic agent, you should use the solution immediately and not store the vial for later.

Acidic solvents

Some peptides — particularly those with high isoelectric points or strongly hydrophobic sequences — will not dissolve cleanly in neutral water. A dilute acetic acid solution (1–10%) is the usual workaround. Check the product spec tab before ordering; we flag the handful of compounds in the catalog that benefit from an acidic reconstitution.

Practical tips

• Warm the solvent to room temperature before use — cold water dissolves poorly.
• Point the solvent stream at the wall of the vial, not directly at the powder cake.
• Gently swirl; do not shake. Agitation creates foam and can denature sensitive sequences.
• Let the vial stand for 2–5 minutes after adding the solvent to complete dissolution.