Protein Concentration (Bradford) Calculator Formula
Understand the math behind the protein concentration (bradford) calculator. Each variable explained with a worked example.
Formulas Used
Protein Concentration
conc_undiluted = (absorbance - intercept) / slope * dilutionProtein Concentration
conc_mg = (absorbance - intercept) / slope * dilution / 1000Variables
| Variable | Description | Default |
|---|---|---|
absorbance | Absorbance at 595 nm | 0.45 |
slope | Calibration Slope (m) | 0.05 |
intercept | Calibration Intercept (b) | 0.02 |
dilution | Dilution Factor | 1 |
How It Works
Bradford Protein Assay
The Bradford assay uses Coomassie Brilliant Blue G-250 dye, which shifts from red to blue upon binding protein. Absorbance at 595 nm is proportional to protein concentration.
Calculation
[Protein] = (A595 - b) / m × dilution factor
where m and b come from a standard curve using BSA or another reference protein. The Bradford assay is sensitive to 1-20 ug/mL but has protein-to-protein variation.
Worked Example
A Bradford assay reads A595 = 0.45, standard curve: m = 0.05, b = 0.02, no dilution.
- 01[Protein] = (0.45 - 0.02) / 0.05 × 1
- 02[Protein] = 0.43 / 0.05 = 8.60 ug/mL
Frequently Asked Questions
What is the linear range of the Bradford assay?
Standard Bradford: 100-1500 ug/mL. Micro Bradford: 1-25 ug/mL. Above the linear range, the curve flattens and concentrations are underestimated. Always dilute high-concentration samples.
What interferes with the Bradford assay?
Detergents (SDS, Triton X-100), strong acids or bases, and high salt concentrations can interfere. Basic amino acids (arginine, lysine, histidine) contribute most to the color response.
How does Bradford compare to BCA and UV280?
Bradford is fast and tolerant of reducing agents but protein-variable. BCA is more consistent but incompatible with reducing agents. UV280 requires no reagents but needs pure protein with known extinction coefficient.
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