Bacteriostatic water (BW) is water for injection containing 0.9% benzyl alcohol as a preservative. It is the standard reconstitution solvent for the majority of lyophilised research peptides due to its preservative properties and compatibility with most peptide sequences.
When to Use Bacteriostatic Water
Use bacteriostatic water as the default reconstitution solvent unless the compound's molecular profile indicates incompatibility (see Solvent Selection Guide). BW extends the usable life of reconstituted peptide solutions by inhibiting microbial growth.
Sourcing Requirements
Use commercially prepared, sterile bacteriostatic water from a verified laboratory supplier. Do not prepare bacteriostatic water in-house unless operating within a licensed compounding or manufacturing environment. Verify benzyl alcohol concentration is 0.9% (9mg/ml) on the product label.
Pre-Use Checks
Inspect the vial for particulate matter, cloudiness, or discolouration — reject if any are present.
Check the expiry date — do not use expired solvent.
Verify the seal integrity before opening.
Preparation Procedure
Using aseptic technique, draw the required volume of bacteriostatic water into a sterile syringe.
Inject slowly into the lyophilised peptide vial, directing the solvent stream against the vial wall rather than directly onto the lyophilised cake — this prevents foaming and degradation.
Do not shake. Gently swirl or roll the vial until the lyophilised material has fully dissolved.
Allow the solution to stand for 2–3 minutes if dissolution is incomplete.
Inspect the resulting solution — it should be clear and free from particulate matter.
Storage of Prepared Solutions
Reconstituted peptide solutions prepared with bacteriostatic water should be stored at 2–8°C for short-term use. For longer-term storage, aliquot and freeze at -80°C. Do not store reconstituted solutions at room temperature.
Compatibility Note
Bacteriostatic water is not appropriate for all peptides. Compounds sensitive to benzyl alcohol or those requiring acidic conditions for solubility should be reconstituted using alternative solvents. Refer to the Solvent Selection Guide.
