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Serial Dilutions
Serial dilution is a step-wise dilution of a solution by a select factor. Serial dilutions are used for analytical purposes and as a method to easily dilute a highly concentrated solution. Most serial dilutions are performed by a dilution factor of 10; for instance, 100 μL of stock solution is added to 900 μL of solvent followed by mixing and subsequent repeats of this dilution until the desired molarity is achieved.
Example: Serial Dilution with Dilution Factor of 10
- Take 100 μL of stock solution
- Add to 900 μL of solvent
- Mix thoroughly
- This creates a 10-fold dilution
- Repeat as needed to reach desired concentration
Molarity and Solution Dilution
Molarity is defined as the number of moles of solute dissolved in one liter of solution, expressed in units of moles per liter (M). A stock solution is a concentrated solution prepared to a high molarity. Researchers often prepare stock solutions to conserve space and resources, as these concentrated solutions can be stored for long periods and diluted as needed to make working solutions.
The C1V1=C2V2 Formula
C₁V₁ = C₂V₂
This equation can be rearranged to determine the amount of stock solution required to prepare a working solution at a given volume and concentration:
V₁ = (C₂ × V₂) / C₁
Calculation of Required Stock Solution
Required Stock Solution (L) = (Desired Final Concentration × Desired Total Volume) / Stock Solution Concentration
Once you know the required stock volume, subtract it from the desired total volume to get the solvent volume needed
Practical Tips
- Always mix thoroughly after adding stock solution to solvent
- Use calibrated pipettes and measuring devices for accuracy
- Consider the total volume needed including any volume lost in transfers
- For very dilute solutions, consider serial dilutions instead of direct dilution from stock
- Store diluted solutions appropriately to maintain stability
- Label all dilutions with concentration and preparation date