Research peptides and compounds are supplied as a lyophilised powder rather than a solution. Working with them in the laboratory means introducing a diluent first, and the diluent used for this is almost always bacteriostatic water. Here is what it is and why that is the standard choice.
Why the material is dry to begin with
Lyophilisation — freeze-drying — removes water from the material under vacuum, taking it from frozen solid directly to vapour without passing through a liquid phase.
The reason is stability. Peptides in solution degrade: bonds hydrolyse, chains can aggregate, and the rate of both climbs with temperature and time. Remove the water and those processes slow dramatically. A lyophilised compound stored correctly remains characterised for far longer than the same material in solution, which is why analytical reference material is supplied dry and why the powder sits as a visible cake at the base of the vial.
What bacteriostatic water actually is
Sterile water containing a bacteriostatic preservative — conventionally benzyl alcohol at 0.9%.
The preservative does not sterilise anything. It inhibits bacterial growth rather than eliminating existing contamination, which is a meaningful distinction. What it enables is multiple entries into the same vial. Each entry is an opportunity for contamination, and in plain sterile water any organism introduced can then multiply. The preservative suppresses that.
How it differs from sterile water for injection
The two are frequently confused and are not interchangeable for this purpose.
- Sterile water for injection contains no preservative. It is intended for single use — entered once, then discarded. Nothing prevents growth if organisms are introduced.
- Bacteriostatic water contains the preservative and is designed for repeated withdrawal from one vial over a period.
Where material is prepared once and drawn from over several sessions, bacteriostatic water is the appropriate diluent. That is the ordinary case in analytical work, which is why it is the standard pairing.
Vial sizes and why they differ
Bacteriostatic water is commonly supplied in 3ml and 10ml vials. The choice follows the scale of the preparation rather than any property of the water — a small vial for a single compound, a larger one where several preparations are made from the same source.
The preservative concentration is the same in both. A larger vial is not a stronger one.
Handling and storage
Standard laboratory practice applies. Keep the stopper intact and disinfect it before each entry. Store the vial as directed on its labelling. Once a lyophilised compound has been reconstituted its stability clock restarts — it is a solution again, with the degradation behaviour of a solution — so material in solution is not equivalent to material still dry, however it is stored.
Our compounds carry a storage instruction of 2–8°C, printed on the outer packaging and stated on each product page.
What we supply
A 3ml vial of bacteriostatic water is included with every peptide order. Additional vials are available separately in 3ml and 10ml.
This article describes laboratory handling of analytical reference material. It is not guidance for use in humans or animals.
All compounds are supplied strictly for laboratory research and analytical purposes. Not intended for human or veterinary use.