Protein Concentration Calculator
Calculate protein concentration from spectrophotometer absorbance data using the Beer-Lambert Law
Calculate Protein Concentration
Extinction Coefficient: 210,000 M⁻¹ cm⁻¹
Molecular Mass: 150,000 g/mol
Enter 1 for stock solution, 2 for 1:2 dilution, etc.
Protein Concentration Results
Formula used: C = (A / (ε × b)) × M × n
Parameters: Absorbance: 0, Extinction Coeff: 210000 M⁻¹ cm⁻¹, Pathlength: 1.00 cm
Protein: IgG – Immunoglobin G (MW: 150000 g/mol)
Example Calculation
IgG Protein Analysis Example
Protein: IgG (Extinction coefficient: 210,000 M⁻¹ cm⁻¹, Molecular mass: 150,000 g/mol)
Absorbance: 0.5 at 280 nm
Pathlength: 1 cm
Dilution factor: 10 (1:10 dilution)
Calculation
C = (A / (ε × b)) × M × n
C = (0.5 / (210,000 × 1)) × 150,000 × 10
C = 3.571 mg/mL
💡 Key Points
Proteins typically absorb at 280 nm wavelength
Standard cuvette pathlength is 1 cm
Account for dilution factor in your measurements
Higher extinction coefficients give more sensitive measurements
Clean cuvettes are essential for accurate readings
📚 Common Proteins
Bovine Serum Albumin
Most common protein standard
Immunoglobulin G
Common antibody protein
Lysozyme
Antimicrobial enzyme
Understanding Protein Concentration Calculation
The Beer-Lambert Law
The protein concentration calculator is based on the Beer-Lambert Law, which describes the absorption of light by molecules in solution:
A = ε × b × C
Rearranged for concentration:
C = A / (ε × b)
For proteins, we multiply by molecular mass and dilution factor to get mass concentration in mg/mL.
Parameters Explained
Absorbance (A)
Optical density measured by spectrophotometer, typically at 280 nm for proteins
Extinction Coefficient (ε)
Protein-specific constant describing light absorption strength (M⁻¹ cm⁻¹)
Pathlength (b)
Inner diameter of the cuvette, usually 1 cm for standard cuvettes
Molecular Mass
Atomic mass of the protein in grams per mol (g/mol)
Dilution Factor
Accounts for sample dilution (1 for stock, 2 for 1:2 dilution, etc.)
Measurement Methods
UV Spectrophotometry
Direct measurement of protein absorbance at 280 nm. Most accurate for pure proteins.
Bradford Assay
Colorimetric method using Coomassie dye. Good for protein mixtures and low concentrations.
BCA Assay
Bicinchoninic acid method. Compatible with most detergents and reducing agents.