OD280 Protein Calculator

Calculate protein concentration from A280 absorbance using extinction coefficients

AU
cm
M⁻¹cm⁻¹
Da
fold

Calculation Results

0.00
Molar Concentration (µM)
0.00
Concentration (mg/mL)
0.00
A280 (0.1%, 1cm)
c = A / (ε × l) × dilution factor
Beer-Lambert Law: A = ε × c × l

What is A280 Measurement?

A280 (absorbance at 280 nm) is the standard method for measuring protein concentration. Proteins absorb UV light at 280 nm primarily due to aromatic amino acids: tryptophan, tyrosine, and disulfide bonds from cysteine.

Extinction Coefficients

Common protein extinction coefficients at 280 nm:

  • BSA: 43,824 M⁻¹cm⁻¹
  • IgG: ~210,000 M⁻¹cm⁻¹
  • Lysozyme: 36,000 M⁻¹cm⁻¹
  • Calculate from sequence for accuracy

Amino Acid Contributions

  • Tryptophan: 5,500 M⁻¹cm⁻¹
  • Tyrosine: 1,490 M⁻¹cm⁻¹
  • Cystine (S-S): 125 M⁻¹cm⁻¹
  • Other amino acids have negligible absorption

Best Practices

  • Use buffer as blank reference
  • Keep A280 between 0.1-1.0 for accuracy
  • Account for nucleic acid contamination (A260/A280)
  • Use quartz cuvettes for UV measurements
  • Consider light scattering at high concentrations

Common Applications

  • Protein purification monitoring
  • Column chromatography fractions
  • Concentration determination before assays
  • Quality control in production
  • Dilution calculations

FAQ

Q: Why use 280 nm wavelength?
A: Aromatic amino acids have maximum absorption near 280 nm, making it ideal for protein detection.

Q: What if I don't know the extinction coefficient?
A: Use the sequence-based calculator or estimate using 1 mg/mL ≈ 1.0 A280 for most proteins.