Bacteriostatic water (3 ml)

Bacteriostatic water consists of purified, sterile water containing 0.9% benzyl alcohol as a bacteriostatic preservative.

How does it work?

The term ‘bacteriostatic’ means that the growth of bacteria is inhibited (not necessarily killed). The benzyl alcohol prevents micro-organisms from multiplying, meaning the solution remains usable for longer after being opened. The concentration of 0.9% is high enough to inhibit bacterial growth, but low enough to be compatible with most peptide solutions used in research.

By way of comparison: sterile water without preservatives and saline do not contain any bacteriostatic agent and are therefore generally intended for single use. Bacteriostatic water is therefore the standard choice for peptide reconstitution in research.

Bac water versus sterile water and saline solution

The main difference lies in the preservative. Sterile water for injection and saline solution (0.9% sodium chloride) do not contain benzyl alcohol and are therefore generally intended for single use. Bacteriostatic water does contain a preservative and is therefore the logical choice when a vial is to be used over several days. For single-use applications involving larger volumes, sterile water may actually be more suitable.

Bacteriostatic water is a standardised pharmaceutical excipient and not a research peptide; consequently, there are no efficacy studies as there are for peptides. The composition (sterile water containing 0.9% benzyl alcohol) is described in pharmacopoeia standards such as the USP.

• Function: solvent for lyophilised peptides in research.
• Characteristic: bacteriostatic effect due to benzyl alcohol.
• Application: multiple use of an opened vial within a controlled laboratory environment.

Shelf life after opening

According to the USP monograph and the manufacturer’s labelling, an opened vial is generally used within 28 days of the first puncture and then discarded, regardless of the remaining volume. You should therefore note the date of first use on the label. When purchasing, check the stated grade (USP) and ensure the seal is intact.

As bacteriostatic water directly determines the quality of any peptide solution, it is worth always using a reliable, certified source and handling the vial with care throughout the entire research period.

Bacteriostatic water is used to dissolve powdered research peptides. The steps below describe the laboratory procedure.

1. 1Disinfect the rubber stopper on the water vial and the peptide vial with an alcohol wipe.
2. 2Use an insulin syringe to draw up the required amount of bacteriostatic water.
3. 3Let the water run slowly down the inside wall of the peptide vial; do not aim it directly at the powder.
4. 4Gently swirl the vial until everything has dissolved; do not shake.
5. 5Label the vial with the date and batch number and store it in a cool place.

Combine with insulin syringes and alcohol wipes from the ‘Lab & Accessories’ range to create a complete testing setup.

Part of your experimental setup

Calculate the required volume per vial in advance, so that the concentration of your solution remains consistent across experiments. A well-organised, documented reconstitution workflow improves the reproducibility of your research.

Choose the volume of bacteriostatic water so that you achieve the desired concentration in your calculation; this will prevent calculation and dilution errors later on in the experiment. Store the vial upright and do not touch the surface of the septum.

Store bacteriostatic water at room temperature, away from direct sunlight. There is no need to freeze it.

Practical storage tips

• Unopened: store in a cool, dry place (at a controlled room temperature), away from sources of heat.
• After opening: store in a cool place (2–8 °C) and use within 28 days.
• Keep the stopper clean and disinfect it before each use.
• Check that the solution is clear; do not use cloudy water.

Good hygiene and proper storage extend the shelf life of an opened vial.