Beer-Lambert Protein Calculator Formula
Understand the math behind the beer-lambert protein calculator. Each variable explained with a worked example.
Formulas Used
Molar Concentration
conc_molar = a280 / (extinction * path_length)Mass Concentration
conc_mg = a280 / (extinction * path_length) * mw_protein / 1000Variables
| Variable | Description | Default |
|---|---|---|
a280 | Absorbance at 280 nm | 1 |
extinction | Extinction Coefficient (E)(M⁻¹cm⁻¹) | 43000 |
path_length | Path Length(cm) | 1 |
mw_protein | Protein Molecular Weight(Da) | 45000 |
How It Works
Protein Concentration from A280
UV absorbance at 280 nm is widely used to measure protein concentration. Aromatic residues (Trp, Tyr) and disulfide bonds absorb at this wavelength.
Formula
c (M) = A280 / (epsilon × l)
c (mg/mL) = c (M) × MW / 1000
The extinction coefficient epsilon can be calculated from the amino acid sequence using tools like ProtParam. Typical values range from 10,000 to 100,000 M⁻¹cm⁻¹.
Worked Example
A protein with epsilon = 43,000 M⁻¹cm⁻¹ and MW = 45 kDa, measured A280 = 1.0 in a 1 cm cuvette.
a280 = 1extinction = 43000path_length = 1mw_protein = 45000
- 01c = 1.0 / (43000 × 1) = 2.326 × 10⁻⁵ M = 23.26 uM
- 02c = 23.26 × 10⁻⁶ × 45000 / 1000 = 1.047 mg/mL
Ready to run the numbers?
Open Beer-Lambert Protein Calculator