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How to Calculate Serial Dilutions

by Allan Robinson, Demand Media

    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.

    Items you will need

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

    Step 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.

    Step 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.

    Step 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.

    Step 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.

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    About the Author

    Allan Robinson has written numerous articles for various health and fitness sites. Robinson also has 15 years of experience as a software engineer and has extensive accreditation in software engineering. He holds a bachelor's degree with majors in biology and mathematics.

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