A ten-fold dilution reduces the concentration of a solution or a suspension of virus by a factor of ten that is to one-tenth the original concentration. A series of ten-fold dilutions is described as ten-fold serial dilutions. In this manual, ten-fold serial dilutions are used in titrations of a suspension of Newcastle disease virus to establish the infectivity titre. They are carried out in small sterile test tubes. These tubes are usually made of glass and it is preferable if they have fitted lids to minimize the risk of contamination during the dilution.

A ten-fold dilution

Step 1.

Use a micropipette to dispense 900 mL of the diluent to glass tube.

Step 2.

Use a micropipette to transfer 100 mL of the test solution to the first well. Discard the tip.

Step 3.

Mix by shaking by hand or using a vortex mixer.

Step 4.

The well now contains 100 mL of the original test solution diluted by one tenth in a total volume of 1000 mL.

Figure 26: A ten-fold dilution

Ten-fold serial dilutions

Step 1.

Set up the sterilized glass test tubes in a rack. Label each tube clearly to indicate the dilution of its contents after the ten-fold serial dilution has been carried out.

Step 2.

Use a micropipette to dispense 900 mL of the diluent to all the labeled sterile tubes.

Step 3.

Use a micropipette to transfer 100 mL of the test solution to the first tube and mix. This is the first ten-fold dilution.

Step 4.

Use a micropipette with new sterile tip to carry out a second ten-fold dilution.

Step 5.

Continue the series of ten-fold dilutions until the last tube.

Figure 27: Ten-fold serial dilutions