Reconstitution Solvents in a Laboratory Context

Bacteriostatic water is sterile water containing 0.9% benzyl alcohol as a preservative. The benzyl alcohol inhibits bacterial growth, which is why it is the standard choice when a reconstituted vial will be stored and drawn from more than once. It is supplied in multi-use vials, typically 3 ml, 10 ml or 30 ml. It is unsuitable for a small number of cell-culture applications where benzyl alcohol would interfere, and for those sterile water is used instead.

Sterile water for injection contains no preservative. It is appropriate when a solution will be prepared and used in one session, or when a preservative would be incompatible with the downstream assay. Once opened it should not be stored, since there is nothing to prevent microbial growth.

Some peptides are poorly soluble in plain water. Acidic peptides may dissolve better with a small amount of dilute ammonium bicarbonate or buffer; basic peptides with dilute acetic acid; very hydrophobic sequences may require a small proportion of DMSO or acetonitrile before dilution with water. These are specialist cases, and the supplier's solubility note on the technical data sheet should be followed. All compounds in our catalogue dissolve readily in bacteriostatic or sterile water.

Allow both the peptide vial and the diluent to reach room temperature before opening, to avoid condensation on the cold powder. Introduce the diluent slowly down the inside wall of the vial rather than directly onto the cake, then swirl gently until the solution is clear. Do not shake; vigorous agitation can cause foaming and aggregation. A cloudy solution or visible particulates indicate incomplete dissolution or a problem with the material.

Concentration is the vial content divided by the diluent volume. A 5 mg vial reconstituted with 2 ml gives 2.5 mg/ml, which is 2,500 mcg/ml. Each 0.1 ml of that solution, which is 10 units on a U-100 insulin-type syringe, contains 250 mcg. The same 5 mg vial reconstituted with 1 ml gives 5 mg/ml, or 500 mcg per 0.1 ml. Choosing the diluent volume therefore sets the working concentration; a larger volume gives a more dilute solution that is easier to measure in small increments. Each peptide page on our site includes a reconstitution reference that performs this calculation for any vial content and diluent volume.

Every prepared solution should be labelled with the compound, the batch reference from the vial, the solvent used, the resulting concentration, the date of preparation and the initials of the person who prepared it. Record the same information in the laboratory notebook. Prepared solutions are refrigerated at 2–8 °C, protected from light, and discarded at the end of the period supported by the laboratory's own stability data. This is laboratory practice for research material and does not constitute administration guidance.