Calculating Concentration in a Dilution Series
The concentration in tube #3 (1/5 dilution) is 20 mg/dL when the original concentration was 100 mg/dL.
Understanding Dilution Calculations
When performing a dilution series, the concentration in each tube is calculated by multiplying the original concentration by the dilution factor:
- Final concentration = Original concentration × Dilution factor
In this case:
- Original concentration = 100 mg/dL
- Dilution factor for tube #3 = 1/5 = 0.2
Therefore:
- Concentration in tube #3 = 100 mg/dL × 0.2 = 20 mg/dL
Complete Dilution Series Results
For reference, the concentrations in all tubes would be:
- Tube #1 (1/4 dilution): 100 mg/dL × 0.25 = 25 mg/dL
- Tube #2 (1/2 dilution): 100 mg/dL × 0.5 = 50 mg/dL
- Tube #3 (1/5 dilution): 100 mg/dL × 0.2 = 20 mg/dL
- Tube #4 (1/10 dilution): 100 mg/dL × 0.1 = 10 mg/dL
Practical Applications in Laboratory Settings
This type of calculation is commonly used in laboratory settings for preparing serial dilutions for various applications, including:
- Antimicrobial susceptibility testing 1
- Preparation of drug concentrations for therapeutic drug monitoring 2
- Preparation of allergen dilutions for immunotherapy 1
Common Pitfalls to Avoid
When working with dilution series:
- Always double-check your calculations, especially when working with critical samples
- Ensure proper mixing of solutions to achieve homogeneous concentrations
- Be aware that some solutions may have stability issues at certain dilutions 1
- Remember that dilution factors are expressed as fractions (e.g., 1/5) where the denominator indicates how many parts the final solution represents compared to the original
For laboratory applications requiring precise dilutions, following standardized protocols such as those outlined by the European Society of Clinical Microbiology and Infectious Diseases is recommended 1.