How to Calculate Serial Dilutions

A dilution is a reduction in the concentration of a solution. A serial dilution is a series of repeated dilutions that provides a geometric dilution of the original solution. This is commonly performed in experiments that involve concentration curves on a logarithmic scale. Serial dilutions are used extensively in biochemistry and microbiology.

Things You'll Need

• Three or more test tubes
• Buffer
• Pipette
• Solution

Instructions

1. Fill test tube A with 10 mL of the solution and fill test tube B with 9 mL of a buffer to dilute the original solution. The buffer is typically water, but it also can be other liquids, depending on the solution in test tube A.

2. Draw 1 mL of the solution in test tube A with the pipette, transfer it to test tube B and mix the contents of test tube B. The solution in test B is 10 times more dilute than the solution in test tube A.

3. Fill test tube C with 9 mL of buffer. Transfer 1 mL of the solution in test tube B to test tube C and mix thoroughly. The solution in test tube C is 10 times more dilute than the solution in test tube B.

4. Examine the effects of serial dilution. The solution in test tube C is 10 times more dilute that the solution in test tube B, which is 10 times more dilute than the solution in test tube A. The solution in test tube C is, therefore, 10 x 10 = 100 times more dilute than the solution in test tube A.

5. Calculate the total dilution in a serial dilution. We can generalize the results of Step 4 by saying that the total dilution ratio Dt is given by the equation Dt = D1 x D2 x D3 x ... x Dn, where Di is the dilution ratio of the ith dilution.

References

• The National Health Museum