How Much Bacteriostatic Water for an Oxytocin 2 mg Vial?
A 2 mg vial of Oxytocin reconstituted with 1 mL of bacteriostatic water gives a concentration of 2000 mcg/mL; with 2 mL it gives 1000 mcg/mL. The calculation depends only on the quantity in the vial and the volume of water added, so the figures below apply to any 2 mg vial.
View product →There is no single correct volume. Adding more water does not change how much is in the vial. It spreads the same quantity through a larger volume, which changes how many syringe units correspond to a given amount. The tables on this page use volumes that produce round numbers on a U-100 syringe; other volumes work identically as long as the resulting concentration is written on the vial.
Concentration by water volume
Concentration is the quantity in the vial divided by the water volume. A 2 mg vial holds 2 mg whether it receives 1 mL or 2 mL; only the mcg/mL figure moves. The right-hand column converts each concentration into the number of U-100 units that contain 100 mcg.
| Vial | Bacteriostatic water added | Concentration | Units containing 100 mcg |
|---|---|---|---|
| 2 mg oxytocin | 1 mL | 2000 mcg/mL | 5 units |
| 2 mg | 2 mL | 1000 mcg/mL | 10 units |
Before choosing a larger volume, check that the vial has headspace for it. A 10 mL vial of bacteriostatic water reconstitutes ten 2 mg vials at 1 mL each.
Reading the concentration on a U-100 syringe
A U-100 insulin syringe is graduated in units, and 100 units equal 1 mL. Units are therefore millilitres multiplied by 100: 0.1 mL is 10 units and 0.25 mL is 25 units. A 0.5 mL syringe carries 50 units and a 0.3 mL syringe carries 30 units on the same scale, with finer markings that make small volumes easier to read.
To find the volume that contains a given amount, divide the amount by the concentration. At 2000 mcg/mL (a 2 mg vial with 1 mL of water), the volume that contains 100 mcg is 100 divided by 2000, which is 0.05 mL, or 5 units. The table below runs the same calculation for four arbitrary amounts. They illustrate the arithmetic and nothing else.
| Amount (illustrative) | Volume at 2000 mcg/mL | U-100 units |
|---|---|---|
| 100 mcg | 0.05 mL | 5 units |
| 200 mcg | 0.1 mL | 10 units |
| 400 mcg | 0.2 mL | 20 units |
| 1000 mcg | 0.5 mL | 50 units |
At 1000 mcg/mL, which the same vial gives with 2 mL of water, every volume in the table moves in proportion: a 400 mcg draw measures 40 units instead of 20. Volumes below about 0.1 mL are hard to read accurately on a 1 mL syringe. Either move to a 0.3 mL or 0.5 mL syringe, or reconstitute with more water so that the same mass occupies a larger, more legible volume.
Oxytocin is supplied by Vistara Labs as a lyophilised material for research use. The quantities on this page illustrate the arithmetic of dilution and measurement only.
The Oxytocin vial
Oxytocin is a nonapeptide, nine amino acids closed by a disulphide bridge, and the first peptide hormone ever synthesised in a laboratory. Vistara Labs supplies it as a 2 mg lyophilised vial, the smallest mass in the catalogue, which is why the syringe table below is written in micrograms: 2 mg is 2000 mcg, and at 2 mg/mL every unit on a U-100 syringe holds 20 mcg. Certificates of analysis for the catalogue are published on the Lab Results page.
Oxytocin was first synthesised in 1953 by Vincent du Vigneaud, work that earned him the 1955 Nobel Prize in Chemistry. Clinical oxytocin is measured in international units of activity; the research vial here is labelled by mass, which is why this page works in milligrams and micrograms rather than units of activity. With only 2 mg in the vial, small volumes of water keep the concentration readable, and a 0.3 mL or 0.5 mL syringe makes the smallest draws easier to measure accurately.
Reconstitution technique
Let the vial reach room temperature, swab both stoppers, and run the measured water slowly down the inside wall of the vial rather than onto the powder. Swirl or tilt gently until the cake dissolves, never shake, and give any remaining powder a few minutes to settle into solution. Label the vial with the date and the concentration, then keep it refrigerated at 2 to 8 °C and protected from light. The full method, with the reason behind each step, is in how to reconstitute peptides with bacteriostatic water.
Why the solution should look clear
Properly reconstituted Oxytocin forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. The causes are covered in why peptides gel or go cloudy.
Bacteriostatic water, not sterile water
Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. The difference is explained in bacteriostatic water explained.
Frequently asked questions
How much bacteriostatic water do I add to a 2 mg vial of Oxytocin?
There is no single correct volume. With 1 mL of bacteriostatic water a 2 mg vial of Oxytocin gives 2000 mcg/mL; with 2 mL it gives 1000 mcg/mL. Adding more water does not change the quantity in the vial, it spreads it through a larger volume, so write the concentration you chose on the vial.
How many 2 mg vials does a 10 mL vial of bacteriostatic water cover?
A 10 mL vial of bacteriostatic water reconstitutes ten 2 mg vials at 1 mL each. Check that the peptide vial has headspace for the volume before choosing a larger one.
How many units on a U-100 syringe contain 100 mcg at 2000 mcg/mL?
At 2000 mcg/mL (a 2 mg vial with 1 mL of water), the volume that contains 100 mcg is 100 divided by 2000, which is 0.05 mL, or 5 units. Units are millilitres multiplied by 100, so 0.1 mL is 10 units. The amounts on this page illustrate the arithmetic only.
What should reconstituted Oxytocin look like?
Properly reconstituted Oxytocin forms a clear, colourless solution. Cloudiness, strands or a gel that will not disperse usually mean the water went in too fast or the vial was shaken; haze that appears later points to warm or bright storage. More on the causes in why peptides gel or go cloudy.
Can I use sterile water instead of bacteriostatic water?
Only for a vial that will be accessed once. Bacteriostatic water is sterile water with 0.9% benzyl alcohol, a preservative that allows a refrigerated vial to be accessed more than once; plain sterile water is intended for single access. Details in bacteriostatic water explained.
How should a reconstituted Oxytocin vial be stored?
Refrigerated at 2 to 8 °C, protected from light and labelled with the date and the concentration. Unopened lyophilised vials are kept cold and dark until they are needed. The full storage guide is how to store research peptides.
Work it out for a different vial or concentration
Our peptide calculator opens pre-set for a 2 mg vial with 1 mL of water and marks the 100 mcg draw of 5 units on a syringe diagram. Change the vial size, water volume, amount or syringe and it recalculates.
Products: Oxytocin 2 mg and bacteriostatic water 10 mL.
