Protein Concentration Calculator (A280)
Determine the concentration of a purified protein sample based on its absorbance at 280 nm, molar extinction coefficient, and molecular weight.
Protein Spectrophotometry
Specify absorbance, extinction coefficient, path length, and molecular weight.
Protein Concentration
* Equal to 0.27 g/L.
Expert Tip
Absorbance at 280 nm depends heavily on the presence of aromatic residues (tryptophan, tyrosine, and cystine bonds). For proteins lacking these, colorimetric assays (e.g. BCA or Bradford) are required.
Methodology & Equations
Beer-Lambert Molarity
Molarity is calculated using Beer-Lambert's spectrophotometric equation:
Mass Concentration
Converted from molarity using molecular weight (MW, where g/mol = Da):
How to Calculate Protein Concentration from A280 Absorbance
Absorbance at 280 nm (A280) is commonly used to quantify proteins, depending on their aromatic amino acid content:
Measure A280 Absorbance
Note the spectrophotometric reading at 280 nm.
Find the Extinction Coefficient
Locate the extinction coefficient (e.g. for IgG, it is 1.37 L/g*cm) or molar extinction coefficient and molecular weight.
Calculate Concentration
Using Beer-Lambert law, Concentration (mg/mL) = A280 / Extinction Coefficient.
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