There are situations when practicing the methods in this manual when you will be required to prepare a final volume of a diluted solution from a concentrated stock solution. This will require calculating the volume of the stock solution and the volume of diluent to prepare the diluted solution. These volumes can be calculated from the ratio of the concentration of the stock solution and the concentration of the diluted solution.

A useful formula for calculating dilution volumes is
**C _{1}V_{1 }= C_{2}V_{2}**

**C _{1}**

**V _{1}** = Volume of stock solution

**C _{2}** = Concentration of diluted
solution

**V _{2} **= Volume of diluted solution

Make sure you recognize the units involved.

For C_{1} and C_{2} the units of concentration
(amount/volume) must be the same.

For V_{1} and V_{2} the units of volume must
be the same.

This formula can be applied to all situations requiring dilution of a stock solution.

**Worked example**

This example is taken from a recent I-2 Newcastle disease vaccine trial carried out at the John Francis Virology Laboratory.

Aliquots of I-2 ND vaccine stock were stored at -70°C.
One aliquot had been removed and titrated and had an Infectivity Titre of
10^{9.3} EID_{50} per mL.

On the day of vaccination, a second aliquot of the vaccine
stock was removed and thawed to prepare diluted vaccine. Calculate the volume of
vaccine stock and diluent required to prepare 5 mL of diluted vaccine to give
10^{6 }EID_{50} in a volume of 30 µL (0.03 mL) to be
delivered by eye-drop.

**C _{1}**

**V _{1}** = ?

**C _{2}** = 10

**V _{2} **= 5 mL

**C _{1}V_{1} =
C_{2}V_{2}**

**V _{1} = **(

**V _{1} **= (10

To prepare the diluted vaccine, measure 5 mL of diluent. Use a micropipette to remove 84 µL of diluent and discard. Add 84 µL of undiluted vaccine to the diluent. Mix well.