Microbiology - Serial Dilution

1. An undiluted (stock) solution is termed the 10⁰ dilution. This may be a chemical solution, or a suspension of bacteria or bacteriophage.

2. Typical diluions are 10-fold dilutions; each dilution is 1/10th the concentration of the previous dilution. The first 10-fold dilution is termed the 10^-1 dilution.

3. Each subsequent dilution is made from a previous dilution. Here is a series of 10-fold dilutions:

 Start: 100 mL 100
 100 mL 10-1
 100 mL 10-2
 100 mL 10-3

 Add: +900 mL Buf. +900 mL Buf. +900 mL Buf. +900 mL Buf.
 Yield: 1000 mL 10-1
 1000 mL 10-2
 1000 mL 10-3
 1000 mL 10-4

4. Since 100 mL of the 10-1 dilution is used to make the 10-2 dilution, only 900 mL remains for use.

5. The buffer used for dilution depends on the substance being diluted:

 Substance  Dilution Buffer
 Chemical  Sterile water
 DNA   TE
 Enzyme   Enzyme Dilution Buffer (with Glycerol)
 Bacteriophage P1 5 mM CaCl2, 10 mM MgSO4
 Bacterial cells  0.9% NaCl