BAC Water vs. Acetic Acid: Which Solvent for Reconstitution?
Two solvents come up most often when reconstituting research peptides: bacteriostatic water and dilute acetic acid. They're not interchangeable for every compound. Here's how labs decide.
Bacteriostatic water (0.9% benzyl alcohol)
Bacteriostatic water is sterile water with 0.9% benzyl alcohol added. The benzyl alcohol is bacteriostatic — it inhibits bacterial growth, which is why a reconstituted vial can be drawn from over multiple sessions rather than a single use. It's the default, general-purpose choice for the majority of peptides that dissolve readily in water.
Acetic acid solution (typically 0.6%)
Acetic acid water is used for peptides that are poorly soluble or "sticky" in plain water — the mildly acidic environment helps certain sequences go fully into solution. If a peptide stays cloudy or won't dissolve in bacteriostatic water, a dilute acetic acid solution is the usual next step.
Quick comparison
| Bacteriostatic Water | Acetic Acid (0.6%) | |
|---|---|---|
| Best for | Most water-soluble peptides | Poorly-soluble / "sticky" peptides |
| Multi-use? | Yes (benzyl alcohol inhibits microbes) | Generally single-prep |
| Solubility help | Standard | Improves hard-to-dissolve sequences |
How to choose
Start with bacteriostatic water for general reconstitution and multi-session research. Reach for acetic acid when a compound resists going into solution. When in doubt, check the compound's known solubility characteristics for your protocol.
Stock both: Bacteriostatic Water · Acetic Acid Water. New to the process? Read how to reconstitute research peptides.