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Serial Dilution Formula:
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Serial dilution is a stepwise dilution of a substance in solution, typically used in microbiology to reduce the concentration of microorganisms to a countable range. It's essential for accurate colony counting and microbial enumeration.
The calculator uses the serial dilution formula:
Where:
Explanation: The total dilution factor is the product of all individual dilution steps in the series. For example, three 1:10 dilutions would give a total dilution factor of 10 × 10 × 10 = 1000.
Details: Serial dilution is crucial for obtaining microbial counts within the countable range (30-300 colonies per plate), determining microbial loads in samples, and preparing standards for microbiological assays.
Tips: Enter the initial concentration in CFU/mL and the total dilution factor (must be ≥1). The calculator will determine the final concentration after dilution.
Q1: What's a typical dilution series in microbiology?
A: Common series are 10-fold (1:10) dilutions, but 2-fold or 5-fold dilutions may be used depending on the expected microbial load.
Q2: How do I calculate total dilution factor for multiple steps?
A: Multiply the individual dilution factors. For example, three 1:100 dilutions would be 100 × 100 × 100 = 1,000,000 total DF.
Q3: Why is the countable range 30-300 colonies?
A: Below 30 reduces statistical reliability; above 300 leads to overcrowding and colony merging, making counting inaccurate.
Q4: Can I use this for non-microbial dilutions?
A: Yes, the same principle applies to any serial dilution, though units would change (e.g., mg/mL instead of CFU/mL).
Q5: How should I record dilution factors?
A: Record as negative exponents (10^-1, 10^-2, etc.) or as fractions (1/10, 1/100). Be consistent in your notation.