Molar Absorptivity Table
Molar absorptivity (ε), also called the molar extinction coefficient, is a measure of how strongly a chemical species absorbs light at a given wavelength. It is a key constant in the Beer-Lambert law equation A = εlc and has units of L·mol⁻¹·cm⁻¹.
Molar Absorptivity & Quick Reference
| Compound | λmax (nm) | ε (L·mol⁻¹·cm⁻¹) | Solvent |
|---|---|---|---|
| KMnO₄ | 525 | 2,455 | Water |
| Bromothymol Blue | 430 | 15,300 | Water |
| NADH | 340 | 6,220 | Water |
| p-Nitrophenol | 400 | 18,380 | 0.1 M NaOH |
| Methyl Orange | 464 | 23,600 | Water |
| Crystal Violet | 590 | 87,000 | Water |
| Fluorescein | 490 | 76,900 | 0.1 M NaOH |
| Rhodamine B | 554 | 106,000 | Ethanol |
| Caffeine | 273 | 9,800 | Water |
| DNA (dsDNA) | 260 | 6,600 | TE Buffer |
| BSA (Protein) | 280 | 43,824 | PBS |
| Hemoglobin | 415 | 131,000 | Water |
Common Unit Conversions
Absorbance ↔ Transmittance
A = −log₁₀(T), T = 10−A
Wavelength ↔ Wavenumber
Ṽ̃ = 10⁷ / λ (λ in nm, Ṽ̃ in cm⁻¹)
Wavelength ↔ Frequency
ν = c / λ
Energy
E = hν = hc / λ
Standard Cuvette Path Lengths
- 1 cm(standard)
- 0.5 cm(semi-micro)
- 0.1 cm(micro)
- 0.01 cm(ultra-micro)
- 5 cm & 10 cm(for very dilute solutions)