Question

 

You are given a series of 10 tubes, each of which contain 4 mL of saline. One mL of sample is added to the first tube, and a dilution using 0.5 mL is carried out in the remaining tubes by taking 0.5 mL from the preceding tube. What is the dilution of the fluid in tube 5? in tube 10?

 

Answer 1

Each of tube contains 4 mL of saline. One mL of sample is added to the first tube

The dilution factor (the dilution) is the volume added is divided by the final volume.

DF = Vs /Vf

In the first tube 1 mL sample is added to 4 mL of diluent to get 5 mL of solution,

DF = 1mL/5mL = 1/5 = 1:5

In the remaining nine tubes dilution is carried out by taking 0.5 mL from the preceding tube.

DF = 0.5/4.5 = 1/9 = 1: 9

In serial dilutions, multiply the dilution factors for each step.

To, calculate the dilution of the fluid in tube 5, multiply the dilution factors five times.

DF = 1/5 x 1/9 x 1/9 x 1/9 x 1/9 = 1/32805

1:32805

To, calculate the dilution of the fluid in tube 10, multiply the dilution factors ten times.

The dilution of the fluid in tube 10

DF = 1/5 x 1/9 x 1/9 x 1/9 x 1/9 x 1/9 x 1/9 x 1/9 x 1/9 x 1/9 =1/ 1937102445

1: 1937102445