Bacteriostatic water vs. sterile water in the lab
Most lyophilized peptides are reconstituted in an aqueous solvent before use in the lab. The two most common choices are sterile water and bacteriostatic water. They look the same but behave differently.
Sterile water
Sterile water is purified water with nothing added. It contains no preservative, so once the vial is punctured it can be contaminated by bacteria. It is treated as single-use: open, use, discard.
Bacteriostatic water
Bacteriostatic water is sterile water with 0.9% benzyl alcohol added. Benzyl alcohol suppresses bacterial growth, so the vial can be punctured several times. Multi-use vials are commonly discarded 28 days after first use.
Which one to use
- If you will draw from the same reconstituted vial more than once, bacteriostatic water is the usual choice.
- If benzyl alcohol could interfere with your assay, such as some cell-culture work, use sterile water and treat the solution as single-use.
- Some hydrophobic sequences dissolve poorly in water alone and need a different solvent. Check the compound's solubility before reconstituting a whole vial.
Handling tips
- Add solvent slowly down the side of the vial rather than directly onto the powder.
- Swirl gently to dissolve. Vigorous shaking can cause foaming and aggregation.
- Label the vial with the solvent, volume, and date.